How to Detect URL Changes in JavaScript?

How to Detect URL Changes in JavaScript with Event Listeners

Monitoring URL changes is crucial for many JavaScript applications, particularly those utilizing AJAX and single-page architectures. In this article, we will investigate the various methods available to detect URL changes and explore the most effective approach.

Event Handlers for URL Changes

There are multiple event handlers that can be utilized to track URL changes in JavaScript. The most common ones include:

• 'hashchange' Event: Monitors changes in the portion of the URL following the '#' symbol.
• 'popstate' Event: Activated when the browser's back or forward buttons are used or when the history object is modified (e.g., via pushState or replaceState).

These event handlers provide a reliable way to detect URL changes, but they have limitations. The 'hashchange' event only triggers when the fragment after the '#' changes, while the 'popstate' event may not always fire reliably.

Custom Event for Comprehensive URL Monitoring

To overcome the limitations of existing event handlers, a custom event can be created to monitor all URL changes. By modifying the history object, we can ensure that a custom 'locationchange' event is fired every time the URL is updated through pushState, replaceState, or the popstate event.

Here's the code to implement the custom event:

(() => {
    let oldPushState = history.pushState;
    history.pushState = function pushState() {
        let ret = oldPushState.apply(this, arguments);
        window.dispatchEvent(new Event('pushstate'));
        window.dispatchEvent(new Event('locationchange'));
        return ret;
    };

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

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

With this modification, you can now add an event listener for the 'locationchange' event to detect any URL changes reliably.

Conclusion

Utilizing event handlers or implementing a custom event provides effective methods to monitor URL changes in JavaScript. Each approach has its own advantages and limitations. By understanding these options and choosing the most appropriate approach based on the specific requirements, developers can ensure that their applications respond effectively to URL changes.

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