How to run a function when any XMLHttpRequest is complete?

Question

I\'m working on a project that has several scripts that I cannot change. These scripts update the page via AJAX. When the update is complete I need to run some code.

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Answer 1

Without jQuery, you can hook the open method to attach a listener for each XHR object's readystatechange events at the time the XHR object is opened. Ensure the following code runs before any Ajax occurs:

// save the real open
var oldOpen = XMLHttpRequest.prototype.open;

function onStateChange(event) {
    // fires on every readystatechange ever
    // use `this` to determine which XHR object fired the change event
}

XMLHttpRequest.prototype.open = function() {
    // when an XHR object is opened, add a listener for its readystatechange events
    this.addEventListener("readystatechange", onStateChange)

    // run the real `open`
    oldOpen.apply(this, arguments);
}

Alternatively, if you only care about successful load events, you can listener for that event instead of readystatechange.