HTML: The Living Standard — Edition for Web Developers

Review Draft: search element with form functionality — Last Updated 1 December 2021

1. 1. 7.8 Session history and navigation
      1. 7.8.1 Browsing sessions
      2. 7.8.2 The session history of browsing contexts
      3. 7.8.3 The History interface
      4. 7.8.4 The Location interface

7.8 Session history and navigation

7.8.1 Browsing sessions

7.8.2 The session history of browsing contexts

The sequence of Documents in a browsing context is its session history. Each browsing context, including child browsing contexts, has a distinct session history. A browsing context's session history consists of a flat list of session history entries.

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.

A session history entry is a struct with the following items:

• URL, a URL

• document, a Document or null

  Each entry, when first created, has a Document for its 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 the session history entry is then used to bring a new Document into being to take the place of the original, in the case where the user agent finds itself having to navigate to the entry.

• serialized state, which is serialized state or null, initially null

• policy container, a policy container or null

• scroll restoration mode, a scroll restoration mode, initially "auto"

• scroll position data, which is scroll position data for the document's restorable scrollable regions

• browsing context name, a browsing context name or null, initially null

• persisted user state, which is implementation-defined, initially null

  For example, some user agents might want to persist 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.

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.

A scroll restoration mode indicates whether the user agent should restore the persisted scroll position (if any) when traversing to an entry. A scroll restoration mode is 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

Several contiguous entries in a session history can share the same document. This can occur when the initial entry is reached via normal navigation, and the following entry is added via history.pushState(). Or it can occur via navigation to a fragment.

All entries that share the same document (and that are therefore merely different states of one particular document) are contiguous by definition.

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 the initial entry created upon navigation. However, it can also be one of the contiguous entries that share the same document, as described above.

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.

7.8.3 The History interface

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, "")

Push a new entry into session history with the given data associated. The current entry's URL will be copied over and used for the new entry's URL.

(The second parameter exists for historical reasons, and cannot be omitted; passing the empty string is traditional.)

window.history.pushState(data, "", url)

Push a new entry into session history with the given data associated, and with its URL set to url.

If the current Document cannot have its URL rewritten to url, a "SecurityError" DOMException will be thrown.

(The second parameter exists for historical reasons, and cannot be omitted; passing the empty string is traditional.)

window.history.replaceState(data, "")

Updates the data stored in the current session history entry to data.

(The second parameter exists for historical reasons, and cannot be omitted; passing the empty string is traditional.)

window.history.replaceState(data, "", url)

Updates the data stored in the current session history entry to data, and its URL to url.

If the current Document cannot have its URL rewritten to url, a "SecurityError" DOMException will be thrown.

(The second parameter exists for historical reasons, and cannot be omitted; passing the empty string is traditional.)

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.

A Document document can have its URL rewritten to a URL targetURL if the following algorithm returns true:

1. Let documentURL be document's URL.

2. If targetURL and documentURL differ in their scheme, username, password, host, or port components, then return false.

3. If targetURL's scheme is an HTTP(S) scheme, then return true. (Differences in path, query, and fragment are allowed for http: and https: URLs.)

4. If targetURL's scheme is "file", and targetURL and documentURL differ in their path component, then return false. (Differences in query and fragment are allowed for file: URLs.)

5. If targetURL and documentURL differ in their path component or query components, then return false. (Only differences in fragment are allowed for other types of URLs.)

6. Return true.

<!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>

<!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, "", '?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>

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

7.8.4 The Location interface

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

document.location [ = value ]

window.location [ = value ]

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

Can be set, to navigate to another page.

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.

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.