1. 7.7 Session history and navigation
      1. 7.7.1 The session history of browsing contexts
      2. 7.7.2 The History interface
      3. 7.7.3 Implementation notes for session history
      4. 7.7.4 The Location interface
        1. 7.7.4.1 [[GetPrototypeOf]] ( )
        2. 7.7.4.2 [[SetPrototypeOf]] ( V )
        3. 7.7.4.3 [[IsExtensible]] ( )
        4. 7.7.4.4 [[PreventExtensions]] ( )
        5. 7.7.4.5 [[GetOwnProperty]] ( P )
        6. 7.7.4.6 [[DefineOwnProperty]] ( P, Desc )
        7. 7.7.4.7 [[Get]] ( P, Receiver )
        8. 7.7.4.8 [[Set]] ( P, V, Receiver )
        9. 7.7.4.9 [[Delete]] ( P )
        10. 7.7.4.10 [[OwnPropertyKeys]] ( )

7.7 Session history and navigation

7.7.1 The session history of browsing contexts

The sequence of Documents in a browsing context is its session history. Each browsing context, including nested browsing contexts, has a distinct session history. A browsing context's session history consists of a flat list of session history entries. Each session history entry consists, at a minimum, of a URL, and each entry may in addition have serialized state, a title, a Document object, form data, a scroll restoration mode, a scroll position, a browsing context name, and other information associated with it.

Each entry, when first created, has a Document. However, when a Document is not active, it's possible for it to be discarded to free resources. The URL and other data in a session history entry is then used to bring a new Document into being to take the place of the original, in case the user agent finds itself having to reactivate that Document.

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 serialized state are added to the session history as the user (or script) navigates from page to page.


Each Document object in a browsing context's session history is associated with a unique History object which must all model the same underlying session history.

The history attribute of the Window interface must return the object implementing the History interface for this Window object's associated Document.


Serialized state is a serialization (via StructuredSerializeForStorage) of an object representing a user interface state. We sometimes informally refer to "state objects", which are the objects representing user interface state supplied by the author, or alternately the objects created by deserializing (via StructuredDeserialize) serialized state.

Pages can add serialized state to the session history. These are then deserialized and 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.

Serialized state is 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). 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 pop-up 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. Which entry is the current entry is changed by the algorithms defined in this specification, e.g. during session history traversal.

The current entry is usually an entry for the URL of the Document. However, it can also be one of the entries for serialized state 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.

User agents that persist the value of form controls are encouraged to also persist their directionality (the value of the element's dir attribute). This prevents values from being displayed incorrectly after a history traversal when the user had originally entered the values with an explicit, non-default directionality.

An entry's scroll restoration mode indicates whether the user agent should restore the persisted scroll position (if any) when traversing to it. The scroll restoration mode may be one of the following:

"auto"
The user agent is responsible for restoring the scroll position upon navigation.
"manual"
The page is responsible for restoring the scroll position and the user agent does not attempt to do so automatically

If unspecified, the scroll restoration mode of a new entry must be set to "auto".

Entries that contain serialized state share the same Document as the entry for the page that was active when they were added.

Contiguous entries that differ just by their URLs' fragments 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.

Each Document in a browsing context can also have a latest entry. This is the entry for that Document to which the browsing context's session history was most recently traversed. When a Document is created, it initially has no latest entry.

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.

7.7.2 The History interface

enum ScrollRestoration { "auto", "manual" };

[Exposed=Window]
interface History {
  readonly attribute unsigned long index;
  readonly attribute unsigned long length;
  attribute ScrollRestoration scrollRestoration;
  readonly attribute any state;
  void go(optional long delta = 0);
  void back();
  void forward();
  void pushState(any data, DOMString title, optional USVString? url = null);
  void replaceState(any data, DOMString title, optional USVString? url = null);
};
window . history . index

Returns the index of the current entry of the joint session history within the joint session history.

window . history . length

Returns the number of entries in the joint session history.

window . history . scrollRestoration [ = value ]

Returns the scroll restoration mode of the current entry in the session history.

Can be set, to change the scroll restoration mode of the current entry in the session history.

window . history . state

Returns the current serialized state, deserialized into an object.

window . 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.

window . history . back()

Goes back one step in the joint session history.

If there is no previous page, does nothing.

window . history . forward()

Goes forward one step in the joint session history.

If there is no next page, does nothing.

window . history . pushState(data, title [, url ] )

Pushes the given data onto the session history, with the given title, and, if provided and not null, the given URL.

window . history . replaceState(data, title [, url ] )

Updates the current entry in the session history to have the given data, title, and, if provided and not null, URL.

Support: historyChrome for Android 59+Chrome 5+UC Browser for Android 11.4+iOS Safari 5.0+Firefox 4+IE 10+Samsung Internet 4+Opera Mini NoneSafari 6+Android Browser 4.2+Opera 11.5+Edge 12+

Source: caniuse.com

The joint session history of a top-level browsing context is the union of all the session histories of all browsing contexts of all the fully active Document objects that share that 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. 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).

Since each Document in a browsing context might have a different event loop, the actual state of the joint session history can be somewhat nebulous. For example, two sibling iframe elements could both traverse from one unique origin to another at the same time, so their precise order might not be well-defined; similarly, since they might only find out about each other later, they might disagree about the length of the joint session history.

The index attribute of the History interface, on getting, must return the index of the current entry of the joint session history within the top-level browsing context's joint session history. If this History object is associated with a Document that is not fully active, getting must instead throw a "SecurityError" DOMException.

The length attribute of the History interface, on getting, must return the number of entries in the top-level browsing context's joint session history. If this History object is associated with a Document that is not fully active, getting must instead throw a "SecurityError" DOMException.

The actual entries are not accessible from script.

The scrollRestoration attribute of the History interface, on getting, must return the scroll restoration mode of the current entry in the session history. On setting, the scroll restoration mode of the current entry in the session history must be set to the new value. If this History object is associated with a Document that is not fully active, both getting and setting must instead throw a "SecurityError" DOMException.

The state attribute of the History interface, on getting, must return the last value it was set to by the user agent. If this History object is associated with a Document that is not fully active, getting must instead throw a "SecurityError" DOMException. Initially, its value must be null.

When the go(delta) method is invoked, if delta is 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 delta. If this History object is associated with a Document that is not fully active, invoking must instead throw a "SecurityError" DOMException.

When the back() method is invoked, the user agent must traverse the history by a delta −1. If this History object is associated with a Document that is not fully active, invoking must instead throw a "SecurityError" DOMException.

When the forward() method is invoked, the user agent must traverse the history by a delta +1. If this History object is associated with a Document that is not fully active, invoking must instead throw a "SecurityError" DOMException.


Each top-level browsing context has a session history traversal queue, initially empty, to which tasks can be added.

Each top-level browsing context, when created, must begin running the following algorithm, known as the session history event loop for that top-level browsing context, in parallel:

  1. Wait until this top-level browsing context's session history traversal queue is not empty.

  2. Pull the first task from this top-level browsing context's session history traversal queue, and execute it.

  3. Return to the first step of this algorithm.

The session history event loop helps coordinate cross-browsing-context transitions of the joint session history: since each browsing context might, at any particular time, have a different event loop (this can happen if the user agent has more than one event loop per unit of related browsing contexts), transitions would otherwise have to involve cross-event-loop synchronization.


To traverse the history by a delta delta, the user agent must append a task to this top-level browsing context's session history traversal queue, the task consisting of running the following steps:

  1. 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.

  2. 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.

  3. Let specified browsing context be the browsing context of the specified entry.

  4. If the specified browsing context's active document's unload a document algorithm is currently running, abort these steps.

  5. Queue a task that consists of running the following substeps. The relevant event loop is that of the specified browsing context's active document. The task source for the queued task is the history traversal task source.

    1. If there is an ongoing attempt to navigate specified browsing context that has not yet matured (i.e. it has not passed the point of making its Document the active document), then cancel that attempt to navigate the browsing context.

    2. If the specified browsing context's active document is not the same Document as the Document of the specified entry, then run these substeps:

      1. 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.

      2. Unload the active document of the specified browsing context with the recycle parameter set to false.

    3. 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:

  1. Let document be the unique Document object this History object is associated with.

  2. If document is not fully active, throw a "SecurityError" DOMException.

  3. Optionally, abort these steps. (For example, the user agent might disallow calls to these methods 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.)

  4. Let targetRealm be this History object's relevant Realm.

  5. Let serializedData be StructuredSerializeForStorage(data). Rethrow any exceptions.

  6. If the third argument is not null, run these substeps:

    1. Parse the value of the third argument, relative to the relevant settings object of this History object.
    2. If that fails, throw a "SecurityError" DOMException and abort these steps.
    3. Let new URL be the resulting URL record.

    4. Compare new URL to document's URL. If any component of these two URL records differ other than the path, query, and fragment components, then throw a "SecurityError" DOMException and abort these steps.
    5. If the origin of new URL is not same origin with the origin of document, and either the path or query components of the two URL records compared in the previous step differ, throw a "SecurityError" DOMException and abort these steps. (This prevents sandboxed content from spoofing other pages on the same origin.)
  7. If the third argument is null, then let new URL be the URL of the current entry.

  8. If the method invoked was the pushState() method:

    1. 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.

    2. Remove any tasks queued by the history traversal task source that are associated with any Document objects in the top-level browsing context's document family.

    3. 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.

    4. Add a session history entry entry to the session history, after the current entry, with serializedData as the serialized state, the given title as the title, new URL as the URL of the entry, and the scroll restoration mode of the current entry in the session history as the scroll restoration mode.

    5. Update the current entry to be this newly added entry.

    Otherwise, if the method invoked was the replaceState() method:

    1. Update the current entry in the session history so that serializedData is the entry's new serialized state, the given title is the new title, and new URL is the entry's new URL.

  9. If the current entry in the session history represents a non-GET request (e.g. it was the result of a POST submission) then update it to instead represent a GET request.

  10. Set document's URL to new URL.

    Since this is neither a navigation of the browsing context nor a history traversal, it does not cause a hashchange event to be fired.

  11. Let state be StructuredDeserialize(serializedData, targetRealm). If this throws an exception, catch it, ignore the exception, and set state to null.

  12. Set history.state to state.

  13. Set the current entry's Document object's latest entry to the current entry.

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 https://example.com/line?x=5 -->
<html lang="en">
<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 https://example.com/line?x=5 -->
<html lang="en">
<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>
<HTML LANG=EN>
<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>

Most applications want to use the same scroll restoration mode value for all of their history entries. To achieve this they can set the scrollRestoration attribute as soon as possible (e.g., in the first script element in the document's head element) to ensure that any entry added to the history session gets the desired scroll restoration mode.

<head>
  <script>
       if ('scrollRestoration' in history)
            history.scrollRestoration = 'manual';
  </script>
</head>
   

7.7.3 Implementation notes for session history

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.

For both pushState() and replaceState(), user agents are encouraged to prevent abuse of these APIs via too-frequent calls or over-large state objects. As detailed above, the algorithm explicitly allows user agents to ignore any such calls when appropriate.

7.7.4 The Location interface

Each Window object is associated with a unique instance of a Location object, allocated when the Window object is created.

The Location exotic object is defined through a mishmash of IDL, invocation of JavaScript internal methods post-creation, and overridden JavaScript internal methods. Coupled with its scary security policy, please take extra care while implementing this excrescence.

To create a Location object, run these steps:

  1. Let location be a new Location platform object.

  2. Perform ! location.[[DefineOwnProperty]]("valueOf", { [[Value]]: %ObjProto_valueOf%, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }).

  3. Perform ! location.[[DefineOwnProperty]](@@toPrimitive, { [[Value]]: undefined, [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }).

  4. Set the value of the [[DefaultProperties]] internal slot of location to location.[[OwnPropertyKeys]]().

  5. Return location.

The addition of valueOf and @@toPrimitive own data properties, as well as the fact that all of Location's IDL attributes are marked [Unforgeable], is required by legacy code that consulted the Location interface, or stringified it, to determine the document URL, and then used it in a security-sensitive way. In particular, the valueOf, @@toPrimitive, and [Unforgeable] stringifier mitigations ensure that code such as foo[location] = bar or location + "" cannot be misdirected.

document . location [ = value ]
window . location [ = value ]

Returns a Location object with the current page's location.

Can be set, to navigate to another page.

The Document object's location attribute's getter must return this Document object's relevant global object's Location object, if this Document object is fully active, and null otherwise.

The Window object's location attribute's getter must return this Window object's Location object.

Location objects provide a representation of the URL of the active document of their Document's browsing context, and allow the current entry of the browsing context's session history to be changed, by adding or replacing entries in the history object.

[Exposed=Window]
interface Location { // but see also additional creation steps and overridden internal methods
  [Unforgeable] stringifier attribute USVString href;
  [Unforgeable] readonly attribute USVString origin;
  [Unforgeable] attribute USVString protocol;
  [Unforgeable] attribute USVString host;
  [Unforgeable] attribute USVString hostname;
  [Unforgeable] attribute USVString port;
  [Unforgeable] attribute USVString pathname;
  [Unforgeable] attribute USVString search;
  [Unforgeable] attribute USVString hash;

  [Unforgeable] void assign(USVString url);
  [Unforgeable] void replace(USVString url);
  [Unforgeable] void reload();

  [Unforgeable, SameObject] readonly attribute DOMStringList ancestorOrigins;
};
location . toString()
location . href

Returns the Location object's URL.

Can be set, to navigate to the given URL.

location . origin

Returns the Location object's URL's origin.

location . protocol

Returns the Location object's URL's scheme.

Can be set, to navigate to the same URL with a changed scheme.

location . host

Returns the Location object's URL's host and port (if different from the default port for the scheme).

Can be set, to navigate to the same URL with a changed host and port.

location . hostname

Returns the Location object's URL's host.

Can be set, to navigate to the same URL with a changed host.

location . port

Returns the Location object's URL's port.

Can be set, to navigate to the same URL with a changed port.

location . pathname

Returns the Location object's URL's path.

Can be set, to navigate to the same URL with a changed path.

location . search

Returns the Location object's URL's query (includes leading "?" if non-empty).

Can be set, to navigate to the same URL with a changed query (ignores leading "?").

location . hash

Returns the Location object's URL's fragment (includes leading "#" if non-empty).

Can be set, to navigate to the same URL with a changed fragment (ignores leading "#").

location . assign(url)

Navigates to the given URL.

location . replace(url)

Removes the current page from the session history and navigates to the given URL.

location . reload()

Reloads the current page.

location . ancestorOrigins

Returns a DOMStringList object listing the origins of the ancestor browsing contexts, from the parent browsing context to the top-level browsing context.

A Location object has an associated relevant Document, which is this Location object's associated Document object's browsing context's active document.

A Location object has an associated url, which is this Location object's relevant Document's URL.

A Location object has an associated ancestor origins list. When a Location object is created, its ancestor origins list must be set to a DOMStringList object whose associated list is the list of strings that the following steps would produce:

  1. Let output be a new list of strings.

  2. Let current be the browsing context of the Document with which this Location object is associated.

  3. Loop: If current has no parent browsing context, jump to the step labeled end.

  4. Let current be current's parent browsing context.

  5. Append the serialization of current's active document's origin to output.

  6. Return to the step labeled loop.

  7. End: Return output.

A Location object has an associated Location-object-setter navigate algorithm, which given a url, runs these steps:

  1. If any of the following conditions are met, let replacement flag be unset; otherwise, let it be set:

  2. Location-object navigate, given url and replacement flag.

To Location-object navigate, given a url and replacement flag, run these steps:

  1. The source browsing context is the responsible browsing context specified by the incumbent settings object.

  2. Navigate the browsing context to url, with the exceptions enabled flag set. Rethrow any exceptions.

    If the replacement flag is set or 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.

The href attribute's getter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. Return this Location object's url, serialized.

The href attribute's setter must run these steps:

  1. Parse the given value relative to the entry settings object. If that failed, throw a TypeError exception.

  2. Location-object-setter navigate to the resulting URL record.

The href attribute setter intentionally has no security check.

The origin attribute's getter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. Return the serialization of this Location object's url's origin.

The protocol attribute's getter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. Return this Location object's url's scheme, followed by ":".

The protocol attribute's setter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. Let copyURL be a copy of this Location object's url.

  3. Let possibleFailure be the result of basic URL parsing the given value, followed by ":", with copyURL as url and scheme start state as state override.

    Because the URL parser ignores multiple consecutive colons, providing a value of "https:" (or even "https::::") is the same as providing a value of "https".

  4. If possibleFailure is failure, then throw a "SyntaxError" DOMException.

  5. If copyURL's scheme is not an HTTP(S) scheme, then terminate these steps.

  6. Location-object-setter navigate to copyURL.

The host attribute's getter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. Let url be this Location object's url.

  3. If url's host is null, return the empty string.

  4. If url's port is null, return url's host, serialized.

  5. Return url's host, serialized, followed by ":" and url's port, serialized.

The host attribute's setter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. Let copyURL be a copy of this Location object's url.

  3. If copyURL's cannot-be-a-base-URL flag is set, terminate these steps.

  4. Basic URL parse the given value, with copyURL as url and host state as state override.

  5. Location-object-setter navigate to copyURL.

The hostname attribute's getter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. If this Location object's url's host is null, return the empty string.

  3. Return this Location object's url's host, serialized.

The hostname attribute's setter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. Let copyURL be a copy of this Location object's url.

  3. If copyURL's cannot-be-a-base-URL flag is set, terminate these steps.

  4. Basic URL parse the given value, with copyURL as url and hostname state as state override.

  5. Location-object-setter navigate to copyURL.

The port attribute's getter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. If this Location object's url's port is null, return the empty string.

  3. Return this Location object's url's port, serialized.

The port attribute's setter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. Let copyURL be a copy of this Location object's url.

  3. If copyURL cannot have a username/password/port, then return.

  4. If the given value is the empty string, then set copyURL's port to null.

  5. Otherwise, basic URL parse the given value, with copyURL as url and port state as state override.

  6. Location-object-setter navigate to copyURL.

The pathname attribute's getter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. Let url be this Location object's url.

  3. If url's cannot-be-a-base-URL flag is set, return the first string in url's path.

  4. If url's path is empty, then return the empty string.

  5. Return "/", followed by the strings in url's path (including empty strings), separated from each other by "/".

The pathname attribute's setter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. Let copyURL be a copy of this Location object's url.

  3. If copyURL's cannot-be-a-base-URL flag is set, terminate these steps.

  4. Set copyURL's path to the empty list.

  5. Basic URL parse the given value, with copyURL as url and path start state as state override.

  6. Location-object-setter navigate to copyURL.

The search attribute's getter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. If this Location object's url's query is either null or the empty string, return the empty string.

  3. Return "?", followed by this Location object's url's query.

The search attribute's setter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. Let copyURL be a copy of this Location object's url.

  3. If the given value is the empty string, set copyURL's query to null.

  4. Otherwise, run these substeps:

    1. Let input be the given value with a single leading "?" removed, if any.

    2. Set copyURL's query to the empty string.

    3. Basic URL parse input, with copyURL as url and query state as state override, and the relevant Document's document's character encoding as encoding override.

  5. Location-object-setter navigate to copyURL.

The hash attribute's getter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. If this Location object's url's fragment is either null or the empty string, return the empty string.

  3. Return "#", followed by this Location object's url's fragment.

The hash attribute's setter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. Let copyURL be a copy of this Location object's url.

  3. Let input be the given value with a single leading "#" removed, if any.

  4. Set copyURL's fragment to the empty string.

  5. Basic URL parse input, with copyURL as url and fragment state as state override.

  6. Location-object-setter navigate to copyURL.

Unlike the equivalent API for the a and area elements, the hash attribute's setter does not special case the empty string to remain compatible with deployed scripts.


When the assign(url) method is invoked, the user agent must run the following steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. Parse url relative to the entry settings object. If that failed, throw a "SyntaxError" DOMException.

  3. Location-object navigate to the resulting URL record.

When the replace(url) method is invoked, the user agent must run the following steps:

  1. Parse url relative to the entry settings object. If that failed, throw a "SyntaxError" DOMException.

  2. Location-object navigate to the resulting URL record with the replacement flag set.

The replace() method intentionally has no security check.

When the reload() method is invoked, the user agent must run the appropriate steps from the following list:

If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin

Throw a "SecurityError" DOMException.

If the currently executing task is the dispatch of a resize event in response to the user resizing the browsing context

Repaint the browsing context and abort these steps.

If the browsing context's active document is an iframe srcdoc document

Reprocess the iframe attributes of the browsing context's browsing context container.

If the browsing context's active document has its reload override flag set

Perform an overridden reload, with the browsing context being navigated as the responsible browsing context. Rethrow any exceptions.

Otherwise

Navigate the browsing context to this Location object's relevant Document's URL to perform an entry update of the browsing context's current entry, with the exceptions enabled flag set. The source browsing context must be the browsing context being navigated. This is a reload-triggered navigation. Rethrow any exceptions.

When a user requests that the active document of a browsing context be reloaded through a user interface element, the user agent should navigate the browsing context to the same resource as that Document, to perform an entry update of the browsing context's current entry. This is a reload-triggered navigation. 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 (with the browsing context being reloaded as the source browsing context).


The ancestorOrigins attribute's getter must run these steps:

  1. If this Location object's relevant Document's origin is not same origin-domain with the entry settings object's origin, then throw a "SecurityError" DOMException.

  2. Otherwise, return this Location object's ancestor origins list.

The details of how the ancestorOrigins attribute works are still controversial and might change. See issue #1918 for more information.


As explained earlier, the Location exotic object requires additional logic beyond IDL for security purposes. The internal slot and internal methods Location objects must implement are defined below.

Every Location object has a [[DefaultProperties]] internal slot representing its own properties at time of its creation.

7.7.4.1 [[GetPrototypeOf]] ( )
  1. If ! IsPlatformObjectSameOrigin(this) is true, then return ! OrdinaryGetPrototypeOf(this).

  2. Return null.

7.7.4.2 [[SetPrototypeOf]] ( V )
  1. Return ! SetImmutablePrototype(this, V).

7.7.4.3 [[IsExtensible]] ( )
  1. Return true.

7.7.4.4 [[PreventExtensions]] ( )
  1. Return false.

7.7.4.5 [[GetOwnProperty]] ( P )
  1. If ! IsPlatformObjectSameOrigin(this) is true, then:

    1. Let desc be ! OrdinaryGetOwnProperty(this, P).

    2. If the value of the [[DefaultProperties]] internal slot of this contains P, then set desc.[[Configurable]] to true.

    3. Return desc.

  2. Let property be ! CrossOriginGetOwnPropertyHelper(this, P).

  3. If property is not undefined, return property.

  4. Throw a "SecurityError" DOMException.

7.7.4.6 [[DefineOwnProperty]] ( P, Desc )
  1. If ! IsPlatformObjectSameOrigin(this) is true, then:

    1. If the value of the [[DefaultProperties]] internal slot of this contains P, then return false.

    2. Return ? OrdinaryDefineOwnProperty(this, P, Desc).

  2. Throw a "SecurityError" DOMException.

7.7.4.7 [[Get]] ( P, Receiver )
  1. If ! IsPlatformObjectSameOrigin(this) is true, then return ? OrdinaryGet(this, P, Receiver).

  2. Return ? CrossOriginGet(this, P, Receiver).

7.7.4.8 [[Set]] ( P, V, Receiver )
  1. If ! IsPlatformObjectSameOrigin(this) is true, then return ? OrdinarySet(this, P, Receiver).

  2. Return ? CrossOriginSet(this, P, V, Receiver).

7.7.4.9 [[Delete]] ( P )
  1. If ! IsPlatformObjectSameOrigin(this) is true, then return ? OrdinaryDelete(this, P).

  2. Throw a "SecurityError" DOMException.

7.7.4.10 [[OwnPropertyKeys]] ( )
  1. If ! IsPlatformObjectSameOrigin(this) is true, then return ! OrdinaryOwnPropertyKeys(this).

  2. Return ! CrossOriginOwnPropertyKeys(this).