How Can JavaScript Reliably Detect Changes in the Location Hash During Ajax Navigation?

JavaScript Detection of Location Hash Changes

When utilizing Ajax and hash for navigation, it's often essential to detect changes in the location hash, indicative of navigation state.

Checking on Document Load

Initially, checking the location hash on document load works well. However, when using hash-based navigation and pressing the browser's back button (e.g., transitioning from #456 to #123), the hash change is not readily captured by JavaScript.

Interval Polling Approach

The traditional solution involves setting an interval that continuously checks the current hash and compares it to the previous one. If a difference is detected, a "changed" event is fired, allowing subscribers to respond. This method is not ideal but provides a fallback for browsers that lack native support for this event.

jQuery Solution

For those using jQuery, a more elegant solution is available. jQuery provides the on() function to listen for hashchange events on the window object. This abstraction simplifies the process without requiring knowledge of hashchange support.

jQuery Special Events

However, some browsers may not natively support hashchange events. To address this, jQuery allows for the use of special events. In this case, setup code can be used to check for native browser support. If lacking, a timer is established to poll for changes and trigger the jQuery event. This approach insulates code from support issues.

By implementing these techniques, developers can effectively detect location hash changes and respond accordingly, allowing for robust and responsive hash-based navigation in Ajax applications.

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