Event when window.location.href changes

Question

I'm writing a Greasemonkey script for a site which at some point modifies location.href.

How can I get an event (via window.addEventListener or something similar) when window.location.href changes on a page? I also need access to the DOM of the document pointing to the new/modified url.

I've seen other solutions which involve timeouts and polling, but I'd like to avoid that if possible.

Answer 1

I use this script in my extension "Grab Any Media" and work fine ( like youtube case )

var oldHref = document.location.href;

window.onload = function() {
    var bodyList = document.querySelector("body")

    var observer = new MutationObserver(function(mutations) {
        if (oldHref != document.location.href) {
            oldHref = document.location.href;
            /* Changed ! your code here */
        }
    });
    
    var config = {
        childList: true,
        subtree: true
    };
    
    observer.observe(bodyList, config);
};

With the latest javascript specification

const observeUrlChange = () => {
  let oldHref = document.location.href;
  const body = document.querySelector("body");
  const observer = new MutationObserver(mutations => {
    if (oldHref !== document.location.href) {
      oldHref = document.location.href;
      /* Changed ! your code here */
    }
  });
  observer.observe(body, { childList: true, subtree: true });
};

window.onload = observeUrlChange;

Compressed with OpenAI

window.onload = () => new MutationObserver(mutations => mutations.forEach(() => oldHref !== document.location.href && (oldHref = document.location.href, /* Changed ! your code here */))).observe(document.querySelector("body"), { childList: true, subtree: true });

Answer 2

popstate event:

The popstate event is fired when the active history entry changes. [...] The popstate event is only triggered by doing a browser action such as a click on the back button (or calling history.back() in JavaScript)

So, listening to popstate event and sending a popstate event when using history.pushState() should be enough to take action on href change:

window.addEventListener('popstate', listener);

const pushUrl = (href) => {
  history.pushState({}, '', href);
  window.dispatchEvent(new Event('popstate'));
};

Answer 3

You can't avoid polling, there isn't any event for href change.

Using intervals is quite light anyways if you don't go overboard. Checking the href every 50ms or so will not have any significant effect on performance if you're worried about that.

Answer 4

There is a default onhashchange event that you can use.

Documented HERE

And can be used like this:

function locationHashChanged( e ) {
    console.log( location.hash );
    console.log( e.oldURL, e.newURL );
    if ( location.hash === "#pageX" ) {
        pageX();
    }
}

window.onhashchange = locationHashChanged;

If the browser doesn't support oldURL and newURL you can bind it like this:

//let this snippet run before your hashChange event binding code
if( !window.HashChangeEvent )( function() {
    let lastURL = document.URL;
    window.addEventListener( "hashchange", function( event ) {
        Object.defineProperty( event, "oldURL", { enumerable: true, configurable: true, value: lastURL } );
        Object.defineProperty( event, "newURL", { enumerable: true, configurable: true, value: document.URL } );
        lastURL = document.URL;
    } );
} () );

Answer 5

Through Jquery, just try

$(window).on('beforeunload', function () {
    //your code goes here on location change 
});

By using javascript:

window.addEventListener("beforeunload", function (event) {
   //your code goes here on location change 
});

Refer Document : https://developer.mozilla.org/en-US/docs/Web/Events/beforeunload

Answer 6

In supporting browsers, use the new Navigation API which is currently being implemented as a replacement for the History API:

navigation.addEventListener('navigate', () => {
  console.log('page changed');
});

This already works in Chromium browsers, but Firefox and Safari are currently missing it as of March 2023.

It simplifies the problem considerably, and is being designed specifically with single page applications in mind which is the main sore spot with existing solutions. No more nasty expensive MutationObserver calls!

Answer 7

Have you tried beforeUnload? This event fires immediately before the page responds to a navigation request, and this should include the modification of the href.

    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
    <HTML>
    <HEAD>
    <TITLE></TITLE>
    <META NAME="Generator" CONTENT="TextPad 4.6">
    <META NAME="Author" CONTENT="?">
    <META NAME="Keywords" CONTENT="?">
    <META NAME="Description" CONTENT="?">
    </HEAD>

         <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.3/jquery.min.js" type="text/javascript"></script>
            <script type="text/javascript">
            $(document).ready(function(){
                $(window).unload(
                        function(event) {
                            alert("navigating");
                        }
                );
                $("#theButton").click(
                    function(event){
                        alert("Starting navigation");
                        window.location.href = "http://www.bbc.co.uk";
                    }
                );

            });
            </script>


    <BODY BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#FF0000" VLINK="#800000" ALINK="#FF00FF" BACKGROUND="?">

        <button id="theButton">Click to navigate</button>

        <a href="http://www.google.co.uk"> Google</a>
    </BODY>
    </HTML>

Beware, however, that your event will fire whenever you navigate away from the page, whether this is because of the script, or somebody clicking on a link. Your real challenge, is detecting the different reasons for the event being fired. (If this is important to your logic)

Answer 8

Try this script which will let you run code whenever the URL changes (without a pageload, like an Single Page Application):

var previousUrl = '';
var observer = new MutationObserver(function(mutations) {
  if (location.href !== previousUrl) {
      previousUrl = location.href;
      console.log(`URL changed to ${location.href}`);
    }
});

Answer 9

based on the answer from "Leonardo Ciaccio", modified code is here: i.e. removed for loop and reassign the Body Element if it is removed

window.addEventListener("load", function () {
  let oldHref = document.location.href,
    bodyDOM = document.querySelector("body");
  function checkModifiedBody() {
    let tmp = document.querySelector("body");
    if (tmp != bodyDOM) {
      bodyDOM = tmp;
      observer.observe(bodyDOM, config);
    }
  }
  const observer = new MutationObserver(function (mutations) {
    if (oldHref != document.location.href) {
      oldHref = document.location.href;
      console.log("the location href is changed!");
      window.requestAnimationFrame(checkModifiedBody)
    }
  });
  const config = {
    childList: true,
    subtree: true
  };
  observer.observe(bodyDOM, config);
}, false);

Answer 10

Well there is 2 ways to change the location.href. Either you can write location.href = "y.html", which reloads the page or can use the history API which does not reload the page. I experimented with the first a lot recently.

If you open a child window and capture the load of the child page from the parent window, then different browsers behave very differently. The only thing that is common, that they remove the old document and add a new one, so for example adding readystatechange or load event handlers to the old document does not have any effect. Most of the browsers remove the event handlers from the window object too, the only exception is Firefox. In Chrome with Karma runner and in Firefox you can capture the new document in the loading readyState if you use unload + next tick. So you can add for example a load event handler or a readystatechange event handler or just log that the browser is loading a page with a new URI. In Chrome with manual testing (probably GreaseMonkey too) and in Opera, PhantomJS, IE10, IE11 you cannot capture the new document in the loading state. In those browsers the unload + next tick calls the callback a few hundred msecs later than the load event of the page fires. The delay is typically 100 to 300 msecs, but opera simetime makes a 750 msec delay for next tick, which is scary. So if you want a consistent result in all browsers, then you do what you want to after the load event, but there is no guarantee the location won't be overridden before that.

var uuid = "win." + Math.random();
var timeOrigin = new Date();
var win = window.open("about:blank", uuid, "menubar=yes,location=yes,resizable=yes,scrollbars=yes,status=yes");


var callBacks = [];
var uglyHax = function (){
    var done = function (){
        uglyHax();
        callBacks.forEach(function (cb){
            cb();
        });
    };
    win.addEventListener("unload", function unloadListener(){
        win.removeEventListener("unload", unloadListener); // Firefox remembers, other browsers don't
        setTimeout(function (){
            // IE10, IE11, Opera, PhantomJS, Chrome has a complete new document at this point
            // Chrome on Karma, Firefox has a loading new document at this point
            win.document.readyState; // IE10 and IE11 sometimes fails if I don't access it twice, idk. how or why
            if (win.document.readyState === "complete")
                done();
            else
                win.addEventListener("load", function (){
                    setTimeout(done, 0);
                });
        }, 0);
    });
};
uglyHax();


callBacks.push(function (){
    console.log("cb", win.location.href, win.document.readyState);
    if (win.location.href !== "http://localhost:4444/y.html")
        win.location.href = "http://localhost:4444/y.html";
    else
        console.log("done");
});
win.location.href = "http://localhost:4444/x.html";

If you run your script only in Firefox, then you can use a simplified version and capture the document in a loading state, so for example a script on the loaded page cannot navigate away before you log the URI change:

var uuid = "win." + Math.random();
var timeOrigin = new Date();
var win = window.open("about:blank", uuid, "menubar=yes,location=yes,resizable=yes,scrollbars=yes,status=yes");


var callBacks = [];
win.addEventListener("unload", function unloadListener(){
    setTimeout(function (){
        callBacks.forEach(function (cb){
            cb();
        });
    }, 0);
});


callBacks.push(function (){
    console.log("cb", win.location.href, win.document.readyState);
    // be aware that the page is in loading readyState, 
    // so if you rewrite the location here, the actual page will be never loaded, just the new one
    if (win.location.href !== "http://localhost:4444/y.html")
        win.location.href = "http://localhost:4444/y.html";
    else
        console.log("done");
});
win.location.href = "http://localhost:4444/x.html";

If we are talking about single page applications which change the hash part of the URI, or use the history API, then you can use the hashchange and the popstate events of the window respectively. Those can capture even if you move in history back and forward until you stay on the same page. The document does not changes by those and the page is not really reloaded.

Answer 11

ReactJS and other SPA applications use the history object

You can listen to window.history updating with the following code:

function watchHistoryEvents() {
    const { pushState, replaceState } = window.history;

    window.history.pushState = function (...args) {
        pushState.apply(window.history, args);
        window.dispatchEvent(new Event('pushState'));
    };

    window.history.replaceState = function (...args) {
        replaceState.apply(window.history, args);
        window.dispatchEvent(new Event('replaceState'));
    };

    window.addEventListener('popstate', () => console.log('popstate event'));
    window.addEventListener('replaceState', () => console.log('replaceState event'));
    window.addEventListener('pushState', () => console.log('pushState event'));
}
watchHistoryEvents();

Answer 12

Also, I found a useful solution with MutationObserver:

function watchLocation() {
    const observable = () => document.location.pathname;

    let oldValue = observable();
    const observer = new MutationObserver(() => {
        const newValue = observable();

        if (oldValue !== newValue) {
            console.log(`changed: ${oldValue} -> ${newValue}`);
            oldValue = newValue;
        }
    });

    observer.observe(document.body, { childList: true, subtree: true });
}

MutationObserver API Documantation