Manipulating the browser history

The DOM  object provides access to the browser's history through the  object. It exposes useful methods and properties that let you move back and forth through the user's history, as well as -- starting with HTML5 -- manipulate the contents of the history stack.

Traveling through history

Moving backward and forward through the user's history is done using the back(), forward(), and go() methods.

Moving forward and backward

To move backward through history, just do:

window.history.back();

This will act exactly like the user clicked on the Back button in their browser toolbar.

Similarly, you can move forward (as if the user clicked the Forward button), like this:

window.history.forward();

Moving to a specific point in history

You can use the go() method to load a specific page from session history, identified by its relative position to the current page (with the current page being, of course, relative index 0).

To move back one page (the equivalent of calling back()):

window.history.go(-1);

To move forward a page, just like calling forward():

window.history.go(1);

Similarly, you can move forward 2 pages by passing 2, and so forth.

You can determine the number of pages in the history stack by looking at the value of the length property:

var numberOfEntries = window.history.length;

Adding and modifying history entries

HTML5 introduced the and history.replaceState() methods, which allow you to add and modify history entries, respectively. These methods work in conjunction with the  event.

Using history.pushState() changes the referrer that gets used in the HTTP header for  objects created after you change the state. The referrer will be the URL of the document whose window is this at the time of creation of the object.

Example

Suppose http://mozilla.org/foo.html executes the following JavaScript:

var stateObj = { foo: "bar" };history.pushState(stateObj, "page 2", "bar.html");

This will cause the URL bar to display http://mozilla.org/bar.html, but won't cause the browser to load bar.html or even check that bar.html exists.

Suppose now that the user now navigates to http://google.com, then clicks back. At this point, the URL bar will displayhttp://mozilla.org/bar.html, and the page will get a popstate event whose state object contains a copy of stateObj. The page itself will look like foo.html, although the page might modify its contents during the popstate event.

If we click back again, the URL will change to http://mozilla.org/foo.html, and the document will get another popstate event, this time with a null state object. Here too, going back doesn't change the document's contents from what they were in the previous step, although the document might update its contents manually upon receiving the popstate event.

The pushState() method

pushState() takes three parameters: a state object, a title (which is currently ignored), and (optionally) a URL. Let's examine each of these three parameters in more detail:

• state object — The state object is a JavaScript object which is associated with the new history entry created bypushState(). Whenever the user navigates to the new state, a popstate event is fired, and the state property of the event contains a copy of the history entry's state object.

  The state object can be anything that can be serialized. Because Firefox saves state objects to the user's disk so they can be restored after the user restarts the browser, we impose a size limit of 640k characters on the serialized representation of a state object. If you pass a state object whose serialized representation is larger than this to pushState(), the method will throw an exception. If you need more space than this, you're encouraged to use sessionStorage and/orlocalStorage.

• title — Firefox currently ignores this parameter, although it may use it in the future. Passing the empty string here should be safe against future changes to the method. Alternatively, you could pass a short title for the state to which you're moving.

• URL — The new history entry's URL is given by this parameter. Note that the browser won't attempt to load this URL after a call to pushState(), but it might attempt to load the URL later, for instance after the user restarts the browser. The new URL does not need to be absolute; if it's relative, it's resolved relative to the current URL. The new URL must be of the same origin as the current URL; otherwise, pushState() will throw an exception. This parameter is optional; if it isn't specified, it's set to the document's current URL.

In a sense, calling pushState() is similar to setting window.location = "#foo", in that both will also create and activate another history entry associated with the current document. But pushState() has a few advantages:

• The new URL can be any URL in the same origin as the current URL. In contrast, setting window.location keeps you at the same  only if you modify only the hash.
• You don't have to change the URL if you don't want to. In contrast, setting window.location = "#foo"; only creates a new history entry if the current hash isn't #foo.
• You can associate arbitrary data with your new history entry. With the hash-based approach, you need to encode all of the relevant data into a short string.
• If title is subsequently used by browsers, this data can be utilized (independent of, say, the hash).

Note that pushState() never causes a hashchange event to be fired, even if the new URL differs from the old URL only in its hash.

The replaceState() method

history.replaceState() operates exactly like history.pushState() except that replaceState() modifies the current history entry instead of creating a new one. Note that this doesn't prevent the creation of a new entry in the global browser history.

replaceState() is particularly useful when you want to update the state object or URL of the current history entry in response to some user action.

The popstate event

A popstate event is dispatched to the window every time the active history entry changes. If the history entry being activated was created by a call to pushState or affected by a call to replaceState, the popstate event's state property contains a copy of the history entry's state object.

See  for sample usage.

Reading the current state

When your page loads, it might have a non-null state object.  This can happen, for example, if the page sets a state object (usingpushState() or replaceState()) and then the user restarts their browser.  When your page reloads, the page will receive anonload event, but no popstate event.  However, if you read the history.state property, you'll get back the state object you would have gotten if a popstate had fired.

You can read the state of the current history entry without waiting for a popstate event using the history.state property like this:

var currentState = history.state;