The sequence of Documents in a browsing
context is its session history.
History objects provide a representation of the
pages in the session history of browsing contexts. Each browsing
context, including nested browsing contexts, has a distinct session
history.
Each Document object in a browsing
context's session history is associated with a
unique instance of the History object, although they
all must model the same underlying session history.
The history attribute
of the Window interface must return the object
implementing the History interface for that
Window object's Document.
History objects represent their browsing
context's session history as a flat list of session history entries. Each
session history entry consists of either a
URL or a state object, or both, and may in addition have a title, a
Document object, form data, a scroll position, and
other information associated with it.
This does not imply that the user interface need be linear. See the notes below.
Titles associated with session history entries need not have any relation
with the current title of the
Document. The title of a session history
entry is intended to explain the state of the document at
that point, so that the user can navigate the document's
history.
URLs without associated state objects are added to the session history as the user (or script) navigates from page to page.
A state object is an object representing a user interface state.
Pages can add state objects between their entry in the session history and the next ("forward") entry. These are then returned to the script when the user (or script) goes back in the history, thus enabling authors to use the "navigation" metaphor even in one-page applications.
State objects are intended to
be used for two main purposes: first, storing a preparsed
description of the state in the URL so that in the
simple case an author doesn't have to do the parsing (though one
would still need the parsing for handling URLs passed around by users, so it's only a minor
optimization), and second, so that the author can store state that
one wouldn't store in the URL because it only applies to the current
Document instance and it would have to be reconstructed
if a new Document were opened.
An example of the latter would be something like keeping track of
the precise coordinate from which a popup div was made
to animate, so that if the user goes back, it can be made to animate
to the same location. Or alternatively, it could be used to keep a
pointer into a cache of data that would be fetched from the server
based on the information in the URL, so that when going
back and forward, the information doesn't have to be fetched
again.
At any point, one of the entries in the session history is the
current entry. This is the entry representing the
active document of the browsing
context. The current entry is usually an entry
for the location of the
Document. However, it can also be one of the entries
for state objects added to the
history by that document.
An entry with persisted user state is one that also has user-agent defined state. This specification does not specify what kind of state can be stored.
For example, some user agents might want to persist the scroll position, or the values of form controls.
Entries that consist of state
objects share the same Document as the entry for
the page that was active when they were added.
Contiguous entries that differ just by fragment identifier also
share the same Document.
All entries that share the same
Document (and that are therefore merely different
states of one particular document) are contiguous by definition.
User agents may discard
the Document objects of entries other than the
current entry that are not referenced from any script,
reloading the pages afresh when the user or script navigates back to
such pages. This specification does not specify when user agents
should discard Document objects and when they should
cache them.
Entries that have had their Document objects
discarded must, for the purposes of the algorithms given below, act
as if they had not. When the user or script navigates back or
forwards to a page which has no in-memory DOM objects, any other
entries that shared the same Document object with it
must share the new object as well.
History interfaceinterface History {
readonly attribute long length;
readonly attribute any state;
void go(in optional long delta);
void back();
void forward();
void pushState(in any data, in DOMString title, in optional DOMString url);
void replaceState(in any data, in DOMString title, in optional DOMString url);
};history . lengthReturns the number of entries in the joint session history.
history . stateReturns the current state object.
history . go( [ delta ] )Goes back or forward the specified number of steps in the joint session history.
A zero delta will reload the current page.
If the delta is out of range, does nothing.
history . back()Goes back one step in the joint session history.
If there is no previous page, does nothing.
history . forward()Goes forward one step in the joint session history.
If there is no next page, does nothing.
history . pushState(data, title [, url ] )Pushes the given data onto the session history, with the given title, and, if provided, the given URL.
history . replaceState(data, title [, url ] )Updates the current entry in the session history to have the given data, title, and, if provided, URL.
The joint session history of a History
object is the union of all the session
histories of all browsing
contexts of all the fully active
Document objects that share the History
object's top-level browsing context, with all the
entries that are current entries
in their respective session
histories removed except for the current entry of the
joint session history.
The current entry of the joint session history is the entry that most recently became a current entry in its session history.
Entries in the joint session history are ordered chronologically by the time they were added to their respective session histories. (Since all these browsing contexts by definition share an event loop, there is always a well-defined sequential order in which their session histories had their entries added.) Each entry has an index; the earliest entry has index 0, and the subsequent entries are numbered with consecutively increasing integers (1, 2, 3, etc).
The length
attribute of the History interface must return the
number of entries in the joint session history.
The actual entries are not accessible from script.
The state
attribute of the History interface must return the last
value it was set to by the user agent. Initially, its value must be
null.
When the go(delta) method is invoked, if the
argument to the method was omitted or has the value zero, the user
agent must act as if the location.reload() method was
called instead. Otherwise, the user agent must traverse the
history by a delta whose value is the value of the method's
argument.
When the back()
method is invoked, the user agent must traverse the history by
a delta −1.
When the forward()method is
invoked, the user agent must traverse the history by a
delta +1.
To traverse the history by a delta delta, the user agent must queue a task to run the following steps. The task source for the queued task is the history traversal task source.
Let delta be the argument to the method.
If the index of the current entry of the joint session history plus delta is less than zero or greater than or equal to the number of items in the joint session history, then abort these steps.
Let specified entry be the entry in the joint session history whose index is the sum of delta and the index of the current entry of the joint session history.
Let specified browsing context be the browsing context of the specified entry.
If the specified browsing context's
active document is not the same Document
as the Document of the specified
entry, then run these substeps:
Prompt to unload the active document of the specified browsing context. If the user refused to allow the document to be unloaded, then abort these steps.
Unload the active document of the specified browsing context with the recycle parameter set to false.
Traverse the history of the specified browsing context to the specified entry.
When the user navigates through a browsing context, e.g. using a browser's back and forward buttons, the user agent must traverse the history by a delta equivalent to the action specified by the user.
The pushState(data, title, url) method adds a state object entry to
the history.
The replaceState(data, title, url) method updates the state object,
title, and optionally the URL of the current
entry in the history.
When either of these methods is invoked, the user agent must run the following steps:
Let clone data be a structured clone of the specified data. If this throws an exception, then rethrow that exception and abort these steps.
If a third argument is specified, run these substeps:
SECURITY_ERR exception
and abort these steps.SECURITY_ERR exception and abort these
steps.SECURITY_ERR exception and abort
these steps. (This prevents sandboxed content from spoofing other
pages on the same origin.)For the purposes of the comparisons in the above substeps, the <path> and <query> components can only be the same if the URLs are both hierarchical URLs.
If the method invoked was the pushState() method:
Remove all the entries in the browsing context's session history after the current entry. If the current entry is the last entry in the session history, then no entries are removed.
This doesn't necessarily have to affect the user agent's user interface.
Remove any tasks queued by the history traversal task source.
If appropriate, update the current entry to reflect any state that the user agent wishes to persist. The entry is then said to be an entry with persisted user state.
Add a state object entry to the session history, after the current entry, with cloned data as the state object, the given title as the title, and, if the third argument is present, the absolute URL that was found earlier in this algorithm as the URL of the entry.
Update the current entry to be this newly added entry.
Otherwise, if the method invoked was the replaceState() method:
Update the current entry in the session history so that cloned data is the entry's new state object, the given title is the new title, and, if the third argument is present, the absolute URL that was found earlier in this algorithm is the entry's new URL.
If the third argument is present, set the document's current address to the absolute URL that was found earlier in this algorithm.
Since this is neither a navigation of the browsing
context nor a history
traversal, it does not cause a hashchange event to be fired.
Set history.state to
another structured clone of the specified data.
The title is purely advisory. User agents might use the title in the user interface.
User agents may limit the number of state objects added to the
session history per page. If a page hits the UA-defined limit, user
agents must remove the entry immediately after the first entry for
that Document object in the session history after
having added the new entry. (Thus the state history acts as a FIFO
buffer for eviction, but as a LIFO buffer for navigation.)
Consider a game where the user can navigate along a line, such that the user is always at some coordinate, and such that the user can bookmark the page corresponding to a particular coordinate, to return to it later.
A static page implementing the x=5 position in such a game could look like the following:
<!DOCTYPE HTML> <!-- this is http://example.com/line?x=5 --> <title>Line Game - 5</title> <p>You are at coordinate 5 on the line.</p> <p> <a href="?x=6">Advance to 6</a> or <a href="?x=4">retreat to 4</a>? </p>
The problem with such a system is that each time the user clicks, the whole page has to be reloaded. Here instead is another way of doing it, using script:
<!DOCTYPE HTML>
<!-- this starts off as http://example.com/line?x=5 -->
<title>Line Game - 5</title>
<p>You are at coordinate <span id="coord">5</span> on the line.</p>
<p>
<a href="?x=6" onclick="go(1); return false;">Advance to 6</a> or
<a href="?x=4" onclick="go(-1); return false;">retreat to 4</a>?
</p>
<script>
var currentPage = 5; // prefilled by server
function go(d) {
setupPage(currentPage + d);
history.pushState(currentPage, document.title, '?x=' + currentPage);
}
onpopstate = function(event) {
setupPage(event.state);
}
function setupPage(page) {
currentPage = page;
document.title = 'Line Game - ' + currentPage;
document.getElementById('coord').textContent = currentPage;
document.links[0].href = '?x=' + (currentPage+1);
document.links[0].textContent = 'Advance to ' + (currentPage+1);
document.links[1].href = '?x=' + (currentPage-1);
document.links[1].textContent = 'retreat to ' + (currentPage-1);
}
</script>
In systems without script, this still works like the previous example. However, users that do have script support can now navigate much faster, since there is no network access for the same experience. Furthermore, contrary to the experience the user would have with just a naïve script-based approach, bookmarking and navigating the session history still work.
In the example above, the data argument to
the pushState() method
is the same information as would be sent to the server, but in a
more convenient form, so that the script doesn't have to parse the
URL each time the user navigates.
Applications might not use the same title for a session
history entry as the value of the document's
title element at that time. For example, here is a
simple page that shows a block in the title element.
Clearly, when navigating backwards to a previous state the user
does not go back in time, and therefore it would be inappropriate
to put the time in the session history title.
<!DOCTYPE HTML>
<TITLE>Line</TITLE>
<SCRIPT>
setInterval(function () { document.title = 'Line - ' + new Date(); }, 1000);
var i = 1;
function inc() {
set(i+1);
history.pushState(i, 'Line - ' + i);
}
function set(newI) {
i = newI;
document.forms.F.I.value = newI;
}
</SCRIPT>
<BODY ONPOPSTATE="set(event.state)">
<FORM NAME=F>
State: <OUTPUT NAME=I>1</OUTPUT> <INPUT VALUE="Increment" TYPE=BUTTON ONCLICK="inc()">
</FORM>
Location interfaceEach Document object in a browsing
context's session history is associated with a unique
instance of a Location object.
location [ = value ]location [ = value ]Returns a Location object with the current page's location.
Can be set, to navigate to another page.
The location attribute
of the HTMLDocument interface must return the
Location object for that Document object,
if it is in a browsing context, and null otherwise.
The location
attribute of the Window interface must return the
Location object for that Window object's
Document.
Location objects provide a representation of their document's current
address, and allow the current entry of the
browsing context's session history to be changed, by
adding or replacing entries in the history object.
interface Location {
stringifier attribute DOMString href;
void assign(in DOMString url);
void replace(in DOMString url);
void reload();
// URL decomposition IDL attributes
attribute DOMString protocol;
attribute DOMString host;
attribute DOMString hostname;
attribute DOMString port;
attribute DOMString pathname;
attribute DOMString search;
attribute DOMString hash;
// resolving relative URLs
DOMString resolveURL(in DOMString url);
};href [ = value ]Returns the current page's location.
Can be set, to navigate to another page.
assign(url)Navigates to the given page.
replace(url)Removes the current page from the session history and navigates to the given page.
reload()Reloads the current page.
resolveURL(url)Resolves the given relative URL to an absolute URL.
The href
attribute must return the current address of the associated
Document object, as an absolute URL.
On setting, if the Location object's associated
Document object has completely loaded,
then the user agent must act as if the assign() method had been called
with the new value as its argument. Otherwise, the user agent must
act as if the replace()
method had been called with the new value as its argument.
When the assign(url) method is invoked, the UA must
resolve the argument, relative to
the entry script's base
URL, and if that is successful, must
navigate the
browsing context to the specified url. If the browsing context's
session history contains only one
Document, and that was the about:blank
Document created when the browsing context
was created, then the navigation must be done with replacement
enabled.
When the replace(url) method is invoked, the UA must
resolve the argument, relative to
the entry script's base
URL, and if that is successful,
navigate the
browsing context to the specified url with replacement enabled.
Navigation for the assign() and replace() methods must be done
with the browsing
context of the script that invoked the method as the
source browsing context.
If the resolving step of the
assign() and replace() methods is not
successful, then the user agent must instead throw a
SYNTAX_ERR exception.
When the reload() method is
invoked, the user agent must run the appropriate steps from the
following list:
resize event in response to the user
resizing the browsing contextRepaint the browsing context and abort these steps.
iframe srcdoc documentReprocess the
iframe attributes of the browsing
context's browsing context container.
Perform an overridden reload.
Navigate the browsing context to the document's current address with replacement enabled. The source browsing context must be the browsing context being navigated.
When a user requests that the current page of a browsing
context be reloaded through a user interface element, the
user agent should navigate the
browsing context to the same resource as
Document, with replacement enabled. In the
case of non-idempotent methods (e.g. HTTP POST), the user agent
should prompt the user to confirm the operation first, since
otherwise transactions (e.g. purchases or database modifications)
could be repeated. User agents may allow the user to explicitly
override any caches when reloading. If browsing
context's active document's reload
override flag is set, then the user agent may instead perform
an overridden reload rather than the navigation
described in this paragraph.
The Location interface also has the complement of
URL decomposition IDL attributes, protocol, host, port, hostname, pathname, search, and hash. These must follow the rules given for URL
decomposition IDL attributes, with the input being the current address of the
associated Document object, as an absolute
URL (same as the href
attribute), and the common setter
action being the same as setting the href attribute to the new output
value.
The resolveURL(url) method must resolve its url argument, relative
to the entry script's base URL, and if that succeeds, return the resulting
absolute URL. If it fails, it must throw a
SYNTAX_ERR exception instead.
User agents must raise a
SECURITY_ERR exception whenever any of the members of a
Location object are accessed by scripts whose
effective script origin is not the same as the Location object's associated
Document's effective script origin, with
the following exceptions:
href setter, if the
script is running in a browsing context that is
allowed to navigate the browsing context with which
the Location object is associated
replace() method,
if the script is running in a browsing context that is
allowed to navigate the browsing context with which
the Location object is associated
This section is non-normative.
The History interface is not meant to place
restrictions on how implementations represent the session history to
the user.
For example, session history could be implemented in a tree-like
manner, with each page having multiple "forward" pages. This
specification doesn't define how the linear list of pages in the
history object are derived from the
actual session history as seen from the user's perspective.
Similarly, a page containing two iframes has a history object distinct from the
iframes' history
objects, despite the fact that typical Web browsers present the user
with just one "Back" button, with a session history that interleaves
the navigation of the two inner frames and the outer page.
Security: It is suggested that to avoid letting
a page "hijack" the history navigation facilities of a UA by abusing
pushState(), the UA
provide the user with a way to jump back to the previous page
(rather than just going back to the previous state). For example,
the back button could have a drop down showing just the pages in the
session history, and not showing any of the states. Similarly, an
aural browser could have two "back" commands, one that goes back to
the previous state, and one that jumps straight back to the previous
page.
In addition, a user agent could ignore calls to pushState() that are invoked on
a timer, or from event listeners that are not triggered in response
to a clear user action, or that are invoked in rapid succession.
Certain actions cause the browsing context to navigate to a new resource. Navigation always involves source browsing context, which is the browsing context which was responsible for starting the navigation.
For example, following a hyperlink, form submission, and the window.open() and location.assign() methods can all
cause a browsing context to navigate.
A user agent may provide various ways for the user to explicitly cause a browsing context to navigate, in addition to those defined in this specification.
When a browsing context is navigated to a new resource, the user agent must run the following steps:
Release the storage mutex.
If the source browsing context is not the same as the browsing context being navigated, and the source browsing context is not one of the ancestor browsing contexts of the browsing context being navigated, and the browsing context being navigated is not both a top-level browsing context and one of the ancestor browsing contexts of the source browsing context, and the source browsing context had its sandboxed navigation browsing context flag set when its active document was created, then abort these steps.
Otherwise, if the browsing context being navigated is a top-level browsing context, and is one of the ancestor browsing contexts of the source browsing context, and the source browsing context had its sandboxed top-level navigation browsing context flag set when its active document was created, then abort these steps.
In both cases, the user agent may additionally offer to open the new resource in a new top-level browsing context or in the top-level browsing context of the source browsing context, at the user's option, in which case the user agent must navigate that designated top-level browsing context to the new resource as if the user had requested it independently.
If the source browsing context is the same as the browsing context being navigated, and this browsing context has its seamless browsing context flag set, and the browsing context being navigated was not chosen using an explicit self-navigation override, then find the nearest ancestor browsing context that does not have its seamless browsing context flag set, and continue these steps as if that browsing context was the one that was going to be navigated instead.
If there is a preexisting attempt to navigate the browsing context, and the source browsing context is the same as the browsing context being navigated, and that attempt is currently running the unload a document algorithm, and the origin of the URL of the resource being loaded in that navigation is not the same origin as the origin of the URL of the resource being loaded in this navigation, then abort these steps without affecting the preexisting attempt to navigate the browsing context.
If a task queued by the traverse the history by a delta algorithm is running the unload a document algorithm for the active document of the browsing context being navigated, then abort these steps without affecting the unload a document algorithm or the aforementioned history traversal task.
If there is a preexisting attempt to navigate the
browsing context, and either that attempt has not yet
matured (i.e. it has
not passed the point of making its Document the
active document), or that navigation's resource is not
to be fetched using HTTP GET or equivalent, or its
resource's absolute URL differs from this attempt's by
more than the presence, absence, or value of the <fragment> component, then cancel
that preexisting attempt to navigate the browsing
context.
Cancel any preexisting attempt to navigate the browsing context.
If the new resource is to be handled using a mechanism that does not affect the browsing context, e.g. ignoring the navigation request altogether because the specified scheme is not one of the supported protocols, then abort these steps and proceed with that mechanism instead.
Prompt to
unload the Document object. If the user
refused to allow the document to be unloaded, then
these steps must be aborted.
Abort the active document of the browsing context.
If the new resource is to be handled by displaying some sort of inline content, e.g. an error message because the specified scheme is not one of the supported protocols, or an inline prompt to allow the user to select a registered handler for the given scheme, then display the inline content and abort these steps.
In the case of a registered handler being used, the algorithm will be reinvoked with a new URL to handle the request.
If the resource has already been obtained (e.g. because it is
being used to populate an object element's new
child browsing context), then skip this step.
Otherwise:
If the new resource is to be fetched using HTTP GET or equivalent, and there are relevant application caches that are identified by a URL with the same origin as the URL in question, and that have this URL as one of their entries, excluding entries marked as foreign, then get the resource from the most appropriate application cache of those that match.
For example, imagine an HTML page with an associated application cache displaying an image and a form, where the image is also used by several other application caches. If the user right-clicks on the image and chooses "View Image", then the user agent could decide to show the image from any of those caches, but it is likely that the most useful cache for the user would be the one that was used for the aforementioned HTML page. On the other hand, if the user submits the form, and the form does a POST submission, then the user agent will not use an application cache at all; the submission will be made to the network.
Otherwise, fetch the new resource, with the manual redirect flag set.
If the resource is being fetched using a method other than one equivalent to HTTP's GET, or, if the navigation algorithm was invoked as a result of the form submission algorithm, then the fetching algorithm must be invoked from the origin of the active document of the source browsing context, if any.
If the browsing context being navigated is a
child browsing context for an iframe or
object element, then the fetching
algorithm must be invoked from the iframe or
object element's browsing context scope
origin, if it has one.
The fetch algorithm must delay the load event of the browsing context.
At this point, unless this step has already been reached once before in the execution of this instance of the algorithm, the user agents must return to whatever algorithm invoked the navigation steps and must continue these steps asynchronously.
If fetching the resource results in a redirect, and either the URL of the target of the redirect has the same origin as the original resource, or the resource is being obtained using the POST method or a safe method (in HTTP terms), return to the step labeled "fragment identifiers" with the new resource.
Otherwise, if fetching the resource results in a redirect but the URL of the target of the redirect does not have the same origin as the original resource and the resource is being obtained using a method that is neither the POST method nor a safe method (in HTTP terms), then abort these steps. The user agent may indicate to the user that the navigation has been aborted for security reasons.
Wait for one or more bytes to be available or for the user agent to establish that the resource in question is empty. During this time, the user agent may allow the user to cancel this navigation attempt or start other navigation attempts.
If the resource was not fetched from an application cache, and was to be fetched using HTTP GET or equivalent, and its URL matches the fallback namespace of one or more relevant application caches, and the most appropriate application cache of those that match does not have an entry in its online whitelist that has the same origin as the resource's URL and that is a prefix match for the resource's URL, and the user didn't cancel the navigation attempt during the previous step, and the navigation attempt failed (e.g. the server returned a 4xx or 5xx status code or equivalent, or there was a DNS error), then:
Let candidate be the fallback resource specified for the fallback namespace in question. If multiple application caches match, the user agent must use the fallback of the most appropriate application cache of those that match.
If candidate is not marked as foreign, then the user agent must discard the failed load and instead continue along these steps using candidate as the resource. The document's address, if appropriate, will still be the originally requested URL, not the fallback URL, but the user agent may indicate to the user that the original page load failed, that the page used was a fallback resource, and what the URL of the fallback resource actually is.
If the document's out-of-band metadata (e.g. HTTP headers), not counting any type information (such as the Content-Type HTTP header), requires some sort of processing that will not affect the browsing context, then perform that processing and abort these steps.
Such processing might be triggered by, amongst other things, the following:
HTTP 401 responses that do not include a challenge recognized by the user agent must be processed as if they had no challenge, e.g. rendering the entity body as if the response had been 200 OK.
User agents may show the entity body of an HTTP 401 response even when the response do include a recognized challenge, with the option to login being included in a non-modal fashion, to enable the information provided by the server to be used by the user before authenticating. Similarly, user agents should allow the user to authenticate (in a non-modal fashion) against authentication challenges included in other responses such as HTTP 200 OK responses, effectively allowing resources to present HTTP login forms without requiring their use.
Let type be the sniffed type of the resource.
If the user agent has been configured to process resources of the given type using some mechanism other than rendering the content in a browsing context, then skip this step. Otherwise, if the type is one of the following types, jump to the appropriate entry in the following list, and process the resource as described there:
text/html"text/html-sandboxed"+xml"application/xml"text/xml"text/plain"Setting the document's
address: If there is no override URL, then any
Document created by these steps must have its address set to the
URL that was originally to be fetched, ignoring any other data that was
used to obtain the resource (e.g. the entity body in the case of a
POST submission is not part of the document's
address, nor is the URL of the fallback resource in the
case of the original load having failed and that URL having been
found to match a fallback
namespace). However, if there is an override
URL, then any Document created by these steps
must have its address
set to that URL instead.
An override URL
is set when dereferencing a
javascript: URL.
Creating a new
Document object: When a Document
is created as part of the above steps, a new Window
object must be created and associated with the
Document, with one exception: if the browsing
context's only entry in its session history is
the about:blank Document that was added
when the browsing context was created, and navigation
is occurring with replacement enabled, and that
Document has the same origin as the new
Document, then the Window object of that
Document must be used instead, and the document attribute of the
Window object must be changed to point to the new
Document instead.
Otherwise, the document's type is such that the resource will not affect the browsing context, e.g. because the resource is to be handed to an external application. Process the resource appropriately.
Some of the sections below, to which the above algorithm defers
in certain cases, require the user agent to update the session
history with the new page. When a user agent is required to do
this, it must queue a task (associated with the
Document object of the current entry, not
the new one) to run the following steps:
Unload the
Document object of the current entry,
with the recycle parameter set to
false.
Replace the Document of the entry being
updated, and any other entries that referenced the same
document as that entry, with the new
Document.
Traverse the history to the new entry.
This can only happen if the entry being updated
is no the current entry, and can never happen with
replacement enabled. (It happens when the user
tried to traverse to a session history entry that no longer had
a Document object.)
Remove all the entries in the browsing context's session history after the current entry. If the current entry is the last entry in the session history, then no entries are removed.
This doesn't necessarily have to affect the user agent's user interface.
Remove any tasks queued by the history traversal task source.
Append a new entry at the end of the History
object representing the new resource and its
Document object and related state.
Traverse the history to the new entry. If the navigation was initiated with replacement enabled, then the traversal must itself be initiated with replacement enabled.
The navigation algorithm has now matured.
Fragment identifier loop: Spin the event loop for a user-agent-defined amount of time, as desired by the user agent implementor. (This is intended to allow the user agent to optimize the user experience in the face of performance concerns.)
If the Document object has no parser, or its
parser has stopped parsing, or
the user agent has reason to believe the user is no longer
interested in scrolling to the fragment identifier, then abort
these steps.
Scroll to the fragment identifier given in the document's current address. If this fails to find an indicated part of the document, then return to the fragment identifier loop step.
The task source for this task is the networking task source.
When an HTML document is to be loaded in a browsing
context, the user agent must queue a task to
create a Document object, mark it as being
an HTML document, create an
HTML parser, and associate it with the document. Each
task that the networking
task source places on the task queue while the
fetching algorithm runs must then fill
the parser's input stream with the fetched bytes and
cause the HTML parser to perform the appropriate
processing of the input stream.
The input stream converts bytes into characters for use in the tokenizer. This process relies, in part, on character encoding information found in the real Content-Type metadata of the resource; the "sniffed type" is not used for this purpose.
When no more bytes are available, the user agent must queue
a task for the parser to process the implied EOF character,
which eventually causes a load event
to be fired.
After creating the Document object, but before any
script execution, certainly before the parser stops, the user agent must update the session
history with the new page.
Application cache selection happens in the HTML parser.
The task source for the two tasks mentioned in this section must be the networking task source.
When faced with displaying an XML file inline, user agents must
first create a Document object, following
the requirements of the XML and Namespaces in XML recommendations,
RFC 3023, DOM3 Core, and other relevant specifications. [XML] [XMLNS] [RFC3023] [DOMCORE]
The actual HTTP headers and other metadata, not the headers as mutated or implied by the algorithms given in this specification, are the ones that must be used when determining the character encoding according to the rules given in the above specifications. Once the character encoding is established, the document's character encoding must be set to that character encoding.
If the root element, as parsed according to the XML
specifications cited above, is found to be an html
element with an attribute manifest whose value is not the
empty string, then, as soon as the element is inserted into the document, the user
agent must resolve the value of
that attribute relative to that element, and if that is successful,
must run the application cache
selection algorithm with the resulting absolute
URL with any <fragment> component removed as
the manifest URL, and passing in the newly-created
Document. Otherwise, if the attribute is absent, its
value is the empty string, or resolving its value fails, then as
soon as the root element is inserted into the document, the user agent must run
the application cache selection
algorithm with no manifest, and passing in the
Document.
Because the processing of the manifest attribute happens
only once the root element is parsed, any URLs referenced by
processing instructions before the root element (such as <?xml-stylesheet?> and <?xbl?> PIs) will be fetched from the network and
cannot be cached.
User agents may examine the namespace of the root
Element node of this Document object to
perform namespace-based dispatch to alternative processing tools,
e.g. determining that the content is actually a syndication feed and
passing it to a feed handler. If such processing is to take place,
abort the steps in this section, and jump to the next step (labeled
"non-document content") in the navigate steps
above.
Otherwise, then, with the newly created Document,
the user agents must update the session history with the new
page. User agents may do this before the complete document
has been parsed (thus achieving incremental rendering), and
must do this before any scripts are to be executed.
Error messages from the parse process (e.g. XML namespace
well-formedness errors) may be reported inline by mutating the
Document.
When a plain text document is to be loaded in a browsing
context, the user agent should queue a task to
create a Document object, mark it as being
an HTML document, create an
HTML parser, associate it with the document, act as if
the tokenizer had emitted a start tag token with the tag name "pre"
followed by a single U+000A LINE FEED (LF) character, and switch the HTML parser's tokenizer
to the PLAINTEXT state. Each task that the networking task
source places on the task queue while the fetching algorithm runs must then fill the
parser's input stream with the fetched bytes and cause
the HTML parser to perform the appropriate processing
of the input stream.
The rules for how to convert the bytes of the plain text document into actual characters, and the rules for actually rendering the text to the user, are defined in RFC 2046, RFC 3676, and subsequent versions thereof. [RFC2046] [RFC3676]
The document's character encoding must be set to the character encoding used to decode the document.
Upon creation of the Document object, the user agent
must run the application cache
selection algorithm with no manifest, and passing in the
newly-created Document.
When no more bytes are available, the user agent must queue
a task for the parser to process the implied EOF character,
which eventually causes a load event
to be fired.
After creating the Document object, but potentially
before the page has finished parsing, the user agent must
update the session history with the new page.
User agents may add content to the head element of
the Document, e.g. linking to a style sheet or an XBL
binding, providing script, giving the document a title,
etc.
In particular, if the user agent supports the Format=Flowed feature of RFC 3676 then the user
agent would need to apply extra styling to cause the text to wrap
correctly and to handle the quoting feature. This could be performed
using, e.g., an XBL binding or a CSS extension.
The task source for the two tasks mentioned in this section must be the networking task source.
When an image resource is to be loaded in a browsing
context, the user agent should create a
Document object, mark it as being an HTML document, append an
html element to the Document, append a
head element and a body element to the
html element, append an img to the
body element, and set the src attribute of the img
element to the address of the image.
Then, the user agent must act as if it had stopped parsing.
Upon creation of the Document object, the user agent
must run the application cache
selection algorithm with no manifest, and passing in the
newly-created Document.
After creating the Document object, but potentially
before the page has finished fully loading, the user agent must
update the session history with the new page.
User agents may add content to the head element of
the Document, or attributes to the img
element, e.g. to link to a style sheet or an XBL binding, to provide
a script, to give the document a title, etc.
When a resource that requires an external resource to be rendered
is to be loaded in a browsing context, the user agent
should create a Document object, mark it
as being an HTML document,
append an html element to the Document,
append a head element and a body element
to the html element, append an embed to
the body element, and set the src attribute of the
embed element to the address of the resource.
Then, the user agent must act as if it had stopped parsing.
Upon creation of the Document object, the user agent
must run the application cache
selection algorithm with no manifest, and passing in the
newly-created Document.
After creating the Document object, but potentially
before the page has finished fully loading, the user agent must
update the session history with the new page.
User agents may add content to the head element of
the Document, or attributes to the embed
element, e.g. to link to a style sheet or an XBL binding, or to give
the document a title.
When the user agent is to display a user agent page inline in a
browsing context, the user agent should create a
Document object, mark it as being an HTML document, and then either
associate that Document with a custom rendering that is
not rendered using the normal Document rendering rules,
or mutate that Document until it represents the content
the user agent wants to render.
Once the page has been set up, the user agent must act as if it had stopped parsing.
Upon creation of the Document object, the user agent
must run the application cache
selection algorithm with no manifest, passing in the
newly-created Document.
After creating the Document object, but potentially
before the page has been completely set up, the user agent must
update the session history with the new page.
When a user agent is supposed to navigate to a fragment identifier, then the user agent must queue a task to run the following steps:
Remove all the entries in the browsing context's session history after the current entry. If the current entry is the last entry in the session history, then no entries are removed.
This doesn't necessarily have to affect the user agent's user interface.
Remove any tasks queued by the history traversal task source.
Append a new entry at the end of the History
object representing the new resource and its Document
object and related state. Its URL must be set to the
address to which the user agent was navigating. The title must be left
unset.
Traverse the history to the new entry. This will scroll to the fragment identifier given in what is now the document's current address.
If the scrolling fails because the relevant ID has not yet been parsed, then the original navigation algorithm will take care of the scrolling instead, as the last few steps of its update the session history with the new page algorithm.
When the user agent is required to scroll to the fragment identifier, it must change the scrolling position of the document using the scroll an element into view algorithm defined in the CSSOM View specification, or perform some other action, such that the indicated part of the document is brought to the user's attention. If there is no indicated part, then the user agent must not scroll anywhere. [CSSOMVIEW]
The indicated part of the document is the one that the
fragment identifier, if any, identifies. The semantics of the
fragment identifier in terms of mapping it to a specific DOM Node is
defined by the specification that defines the MIME type
used by the Document (for example, the processing of
fragment identifiers for XML MIME
types is the responsibility of RFC3023). [RFC3023]
For HTML documents (and HTML MIME types), the following processing model must be followed to determine what the indicated part of the document is.
Parse the URL, and let fragid be the <fragment> component of the URL.
If fragid is the empty string, then the indicated part of the document is the top of the document; stop the algorithm here.
Let decoded fragid be the result of expanding any sequences of percent-encoded octets in fragid that are valid UTF-8 sequences into Unicode characters as defined by UTF-8. If any percent-encoded octets in that string are not valid UTF-8 sequences, then skip this step and the next one.
If this step was not skipped and there is an element in the DOM that has an ID exactly equal to decoded fragid, then the first such element in tree order is the indicated part of the document; stop the algorithm here.
If there is an a element in the DOM that has a
name attribute whose value is
exactly equal to fragid (not decoded fragid), then the first such element in tree
order is the indicated part of the document; stop the
algorithm here.
If fragid is an ASCII
case-insensitive match for the string top, then the indicated part of the
document is the top of the document; stop the algorithm
here.
Otherwise, there is no indicated part of the document.
For the purposes of the interaction of HTML with Selectors' :target pseudo-class, the
target element is the indicated part of the
document, if that is an element; otherwise there is no
target element. [SELECTORS]
When a user agent is required to traverse the history to a specified entry, optionally with replacement enabled, the user agent must act as follows.
This algorithm is not just invoked when explicitly going back or forwards in the session history — it is also invoked in other situations, for example when navigating a browsing context, as part of updating the session history with the new page.
If there is no longer a Document object for the
entry in question, the user agent must
navigate
the browsing context to the location for that entry to perform an
entry update of that entry, and abort these steps. The
"navigate" algorithm reinvokes this "traverse"
algorithm to complete the traversal, at which point there
is a Document object and so this step gets
skipped. The navigation must be done using the same source
browsing context as was used the first time this entry was
created. (This can never happen with replacement
enabled.)
If the current entry's title was not set by the
pushState() or replaceState() methods,
then set its title to the value returned by the document.title IDL
attribute.
If appropriate, update the current entry in the
browsing context's Document object's
History object to reflect any state that the user
agent wishes to persist. The entry is then said to be an
entry with persisted user state.
If the specified entry has a different
Document object than the current entry
then the user agent must run the following substeps:
Document of the specified entry is not the
same as the origin
of the Document of the current entry,
then the following sub-sub-steps must be run:
Document objects with the same
origin as the active document and
that are contiguous with the current entry.Document object the
active document of the browsing
context.Document objects with the same origin
as the new active document, and that are
contiguous with the specified entry, must be cleared.If the specified entry's
Document has any input elements whose
resulting autocompletion state is off, invoke the reset algorithm of each
of those elements.
If the current document readiness of the
specified entry's Document is "complete",
queue a task to fire a pageshow event at the
Window object of that Document, but
with its target set to the
Document object (and the currentTarget set to the
Window object), using the
PageTransitionEvent interface, with the persisted
attribute set to true. This event must not bubble, must not be
cancelable, and has no default action.
Set the document's current address to the URL of the specified entry.
If the specified entry has a URL whose fragment
identifier differs from that of the current entry's
when compared in a case-sensitive manner, and the two
share the same Document object, then let hash changed be true, and let old
URL be the URL of the current entry and new URL be the URL of the specified entry.
Otherwise, let hash changed be false.
If the traversal was initiated with replacement enabled, remove the entry immediately before the specified entry in the session history.
If the specified entry is not an entry with persisted user state, but its URL has a fragment identifier, scroll to the fragment identifier.
If the entry is an entry with persisted user state, the user agent may update aspects of the document and its rendering, for instance the scroll position or values of form fields, that it had previously recorded.
This can even include updating the dir attribute of textarea
elements or input elements whose type attribute is in either the
Text state or the Search state, if the
persisted state includes the directionality of user input in such
controls.
If the entry is a state object entry, let state be a structured clone of that state object. Otherwise, let state be null.
Set history.state to state.
Fire a popstate event at
the Window object of the Document, using
the PopStateEvent interface, with the state attribute set to the
value of state. This event must bubble but not
be cancelable and has no default action.
If hash changed is true, then fire a
hashchange event at the
browsing context's Window object, using
the HashChangeEvent interface, with the oldURL attribute set to
old URL and the newURL attribute set to
new URL. This event must bubble but not be
cancelable and has no default action.
The current entry is now the specified entry.
The task source for the tasks mentioned above is the DOM manipulation task source.
The popstate event
is fired in certain cases when navigating to a session history
entry.
interface PopStateEvent : Event {
readonly attribute any state;
void initPopStateEvent(in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in any stateArg);
};stateReturns a copy of the information that was provided to pushState() or replaceState().
The initPopStateEvent()
method must initialize the event in a manner analogous to the
similarly-named method in the DOM Events interfaces. [DOMEVENTS]
The state
attribute represents the context information for the event, or null,
if the state represented is the initial state of the
Document.
The hashchange
event is fired when navigating to a session history
entry whose URL differs from that of the
previous one only in the fragment identifier.
interface HashChangeEvent : Event {
readonly attribute DOMString oldURL;
readonly attribute DOMString newURL;
void initHashChangeEvent(in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in DOMString oldURLArg, in DOMString newURLArg);
};oldURLReturns the URL of the session history entry that was previously current.
newURLReturns the URL of the session history entry that is now current.
The initHashChangeEvent()
method must initialize the event in a manner analogous to the
similarly-named method in the DOM Events interfaces. [DOMEVENTS]
The oldURL
attribute represents context information for the event, specifically
the URL of the session history entry that was traversed
from.
The newURL
attribute represents context information for the event, specifically
the URL of the session history entry that was traversed
to.
The pageshow event
is fired when traversing to a session history
entry.
The pagehide
event is fired when traversing from a session history
entry.
interface PageTransitionEvent : Event {
readonly attribute boolean persisted;
void initPageTransitionEvent(in DOMString typeArg, in boolean canBubbleArg, in boolean cancelableArg, in boolean persistedArg);
};persistedReturns false if the page is newly being loaded (and the load event will fire). Otherwise, returns true.
The initPageTransitionEvent()
method must initialize the event in a manner analogous to the
similarly-named method in the DOM Events interfaces. [DOMEVENTS]
The persisted
attribute represents the context information for the event.
A Document has a salvageable state, which
is initially true.
When a user agent is to prompt to unload a document, it must run the following steps.
Let event be a new
BeforeUnloadEvent event object with the name beforeunload, which does not
bubble but is cancelable.
Release the storage mutex.
If any event listeners were triggered by the earlier
dispatch step, then set the Document's salvageable state to
false.
If the returnValue
attribute of the event object is not the empty
string, or if the event was canceled, then the user agent should
ask the user to confirm that they wish to unload the document.
The prompt shown by the user agent may include the string of
the returnValue
attribute, or some leading subset thereof. (A user agent may want
to truncate the string to 1024 characters for display, for
instance.)
The user agent must pause while waiting for the user's response.
If the user did not confirm the page navigation, then the user agent refused to allow the document to be unloaded.
If this algorithm was invoked by another instance of the "prompt to unload a document" algorithm (i.e. through the steps below that invoke this algorithm for all descendant browsing contexts), then abort these steps here.
Let descendants be the list of the
descendant browsing contexts of the
Document.
If descendants is not an empty list, then for each browsing context b in descendants run the following substeps:
Prompt to unload the active document of the browsing context b. If the user refused to allow the document to be unloaded, then the user implicitly also refused to allow this document to be unloaded; abort these steps.
If salvageable state of the active document of the browsing context b is false, then set the salvageable state of this document to false also.
When a user agent is to unload a document, it must run
the following steps. These steps are passed an argument, recycle, which is either true or false, indicating
whether the Document object is going to be
re-used. (This is set by the document.open() method.)
Fire a pagehide event at
the Window object of the Document, but
with its target set to the
Document object (and the currentTarget set to the
Window object), using the
PageTransitionEvent interface, with the persisted
attribute set to true. This event must not bubble, must not be
cancelable, and has no default action.
Unload event: Fire a simple event named
unload at the
Document's Window object.
Release the storage mutex.
If any event listeners were triggered by the earlier
unload event step, then set the Document
object's salvageable state to
false.
Run any unloading document cleanup steps for
Document that are defined by this specification and
other applicable specifications.
If this algorithm was invoked by another instance of the "unload a document" algorithm (i.e. through the steps below that invoke this algorithm for all descendant browsing contexts), then abort these steps here.
Let descendants be the list of the
descendant browsing contexts of the
Document.
If descendants is not an empty list, then for each browsing context b in descendants run the following substeps:
Unload the active document of the browsing context b with the recycle parameter set to false.
If salvageable state of the active document of the browsing context b is false, then set the salvageable state of this document to false also.
If salvageable and recycle are both false, then the
Document's browsing context must discard the
Document.
This specification defines the following unloading document cleanup steps. Other specifications can define more.
Close the WebSocket connection of any
WebSocket objects that were created by the WebSocket() constructor visible on the
Document's Window object. If this
affected any WebSocket objects, the set
Document's salvageable state to
false.
[WEBSOCKET]
If the Document's salvageable state is
false, empty the Document's Window's
list of active timeouts and its list of active
intervals.
interface BeforeUnloadEvent : Event {
attribute DOMString returnValue;
};returnValue [ = value ]Returns the current return value of the event (the message to show the user).
Can be set, to update the message.
There are no BeforeUnloadEvent-specific
initialization methods.
The returnValue
attribute represents the message to show the user. When the event is
created, the attribute must be set to the empty string. On getting,
it must return the last value it was set to. On setting, the
attribute must be set to the new value.
If a Document is aborted, the user agent must run the following
steps:
Abort the active documents of every child browsing context.
Cancel any instances of the fetch
algorithm in the context of this Document, discarding
any tasks queued for them, and discarding any further data
received from the network for them.
If the Document has an active
parser, then abort that
parser.
User agents may allow users to explicitly invoke the abort a document algorithm for a
Document. If the user does so, then, if that
Document is an active document, the user
agent should queue a task to fire a simple
event named abort at that
Document's Window object before invoking
the abort algorithm.