Intercept or catch Ajax Calls with Javascript

Question

Is it possible to create a Javascript and include it in a web page that the function of this JS is to "catch" all GET request or any other Ajax calls made from any other Javascript on the page? Either to log it or just plain show it in a Alert box.

The "other Javacript" that will be executing GET or Ajax calls is arbitrary. I mean I have no control over that in terms of what it is.

And once caught I need to check which Javascript executing which GET or Ajax calls.

Is this possible?

Do you need this for debugging? All major browsers have this built in. — Yoshi
– Yoshi, Commented Mar 29, 2012 at 7:28
For now since it seems that its not easy with plain Javascript maybe I can use browser plugin, however Firebug does not show which Javascript initiated the GET method for example... — quarks
– quarks, Commented Mar 29, 2012 at 7:32
...but my requirement is not really for debugging, but for actual application function. — quarks
– quarks, Commented Mar 29, 2012 at 8:44
Then test @Jasd's solution. It's probably the right direction. Though you'll have to make sure your code runs before the first ajax request. — Yoshi
– Yoshi, Commented Mar 29, 2012 at 8:47

Johannes Egger · Accepted Answer · 2012-03-29 07:13:53Z

12

Try this snippet. It extends the send function so that you can execute something before or after the real sending.

XMLHttpRequest.prototype.reallySend = XMLHttpRequest.prototype.send;
XMLHttpRequest.prototype.send = function(body) {
    // Do something...
    this.reallySend(body);
};
var req = new XMLHttpRequest();
req.open("GET", "any.html", true);
req.send(null);

answered Mar 29, 2012 at 7:13

Johannes Egger

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5 Comments

quarks Over a year ago

This worked and I was able to catch Ajax call, however I did not caught the request for the HTML I was expecting probably because its not Ajax call, do you know how to intercept GET events caused by Javascript?

Yoshi Over a year ago

@xybrek You can use this approach as a template. What you have to do is adept this to every method javascript has to make requests (e.g. the Image Object, <script>-elements, and many more).

Johannes Egger Over a year ago

@xybrek Unfortunately I don't know such an event. Maybe it's best to follow Yoshi's advice to implement the solution for each element which can cause the browser to make a request.

quarks Over a year ago

@Yoshi can you site some example for your approach?

Yoshi Over a year ago

@xybrek sort of similar question: stackoverflow.com/a/9676178/697154 hope it helps

weiya ou · Accepted Answer · 2020-10-11 13:00:02Z

1

const nativeOpen = XMLHttpRequest.prototype.open;

const proxiedOpen = function () {
  if (arguments[1].includes('youUrl.com')) {
    // do some ...
  }
  nativeOpen.apply(this, arguments);
};

Refer to the answer:

Intercept AND CHANGE the results of an ajax call

answered Oct 11, 2020 at 13:00

weiya ou

4,7341 gold badge21 silver badges26 bronze badges

2 Comments

Christophe Over a year ago

why answer a 8 year old question which was resolved...?

weiya ou Over a year ago

I searched for related questions and found this question, so..., more reference answers are not a bad thing.

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