Detect AJAX events with JavaScript

There are times when you might want to monitor AJAX requests made from a page.

The following provides a simple way to monitor AJAX events by TYPE, request URL and response payload.

const originalXMLHttpRequest = XMLHttpRequest.prototype.open
XMLHttpRequest.prototype.open = function (type, url) {
    // do URL matching here if needed
    if (url.indexOf('/some/request/url/you/want/to/listen/to') !== -1) {
        this.addEventListener('load', function () {
            // match some JSON values on responseText
            if (this.responseText.includes('"env_shopOnBehalfSessionEstablished" : "true"') && this.responseText.includes('"env_shopOnBehalfEnabled_CSR" : "true"')) {
                // Do some work
            }
        })
    }
    originalXMLHttpRequest.apply(this, arguments)
}

The following method provides more hooks into XMLHttpRequest if they are needed.

var s_ajaxListener = new Object();
s_ajaxListener.tempOpen = XMLHttpRequest.prototype.open;
s_ajaxListener.tempSend = XMLHttpRequest.prototype.send;
s_ajaxListener.callback = function() {
	console.log(this.method + ':' + this.url + '\n' + this.data);
	if (this.url == 'mypath') {
		// actions
	}
}

XMLHttpRequest.prototype.open = function(a, b) {
	if (!a) var a = '';
	if (!b) var b = '';
	s_ajaxListener.tempOpen.apply(this, arguments);
	s_ajaxListener.method = a;
	s_ajaxListener.url = b;
	if (a.toLowerCase() == 'get') {
		s_ajaxListener.data = b.split('?');
		s_ajaxListener.data = s_ajaxListener.data[1];
	}
}

XMLHttpRequest.prototype.send = function(a, b) {
	if (!a) var a = '';
	if (!b) var b = '';
	s_ajaxListener.tempSend.apply(this, arguments);
	if (s_ajaxListener.method.toLowerCase() == 'post') s_ajaxListener.data = a;
	s_ajaxListener.callback();
}

From: https://stackoverflow.com/questions/3596583/javascript-detect-an-ajax-event