JavaScript - on location changed event / on url changed event

In this short article we would like to show how to detect if page url (location object) was changed with JavaScript.

In JavaScript there is no locationchange event, but there are some tricks how to do it.

Quick solution:

// Put following code on the top of head element:

;(function() {
    var pushState = history.pushState;
    var replaceState = history.replaceState;

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

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

    window.addEventListener('popstate', function() {
        window.dispatchEvent(new Event('locationchange'))
    });
})();

// Example usage:

window.addEventListener('locationchange', function(){
    console.log('onlocationchange event occurred!');
})

Better problem description

With location changed monitoring related are three cases:

1. when url is changed from browser UI by user, whole page is reloaded and there are executed two operations: unload and load page - it is just opening new page,
2. location changed by History API (pushState, replaceState, popState) doesn't cause page reloading. API doesn't provide any locationchange event too. It is necessary to call some logic after the methods, e.g.

   history.pushState(...);
   callEventLogic();
   
   // ...
   
   history.popState(...);
   callEventLogic();
   
   // etc.

3. hash changed in url (location.hash) is provided by separated event:

   window.addEventListener('hashchange', function(){
       console.log('onhashchange event occurred!');
   })

Summary: it is necessary to add own locationchange event support what is mentioned in second point in above list what was presented in Quick solution too.