[javascript] iFrame src change event detection?

Assuming I have no control over the content in the iframe, is there any way that I can detect a src change in it via the parent page? Some sort of onload maybe?

My last resort is to do a 1 second interval test if the iframe src is the same as it was before, but doing this hacky solution would suck.

I'm using the jQuery library if it helps.

Here is the method which is used in Commerce SagePay and in Commerce Paypoint Drupal modules which basically compares document.location.href with the old value by first loading its own iframe, then external one.

So basically the idea is to load the blank page as a placeholder with its own JS code and hidden form. Then parent JS code will submit that hidden form where its #action points to the external iframe. Once the redirect/submit happens, the JS code which still running on that page can track your document.location.href value changes.

Here is example JS used in iframe:

;(function($) {
  Drupal.behaviors.commercePayPointIFrame = {
    attach: function (context, settings) {
      if (top.location != location) {
        $('html').hide();
        top.location.href = document.location.href;
      }
    }
  }
})(jQuery);

And here is JS used in parent page:

;(function($) {
  /**
   * Automatically submit the hidden form that points to the iframe.
   */
  Drupal.behaviors.commercePayPoint = {
    attach: function (context, settings) {
      $('div.payment-redirect-form form', context).submit();
      $('div.payment-redirect-form #edit-submit', context).hide();
      $('div.payment-redirect-form .checkout-help', context).hide();
    }
  }
})(jQuery);

Then in temporary blank landing page you need to include the form which will redirect to the external page.

The iframe always keeps the parent page, you should use this to detect in which page you are in the iframe:

Html code:

<iframe id="iframe" frameborder="0" scrolling="no" onload="resizeIframe(this)" width="100%" src="www.google.com"></iframe>

Js:

    function resizeIframe(obj) {
        alert(obj.contentWindow.location.pathname);
    }

Since version 3.0 of Jquery you might get an error

TypeError: url.indexOf is not a function

Which can be easily fix by doing

$('#iframe').on('load', function() {
    alert('frame has (re)loaded ');
});

Answer based on JQuery < 3

$('#iframeid').load(function(){
    alert('frame has (re)loaded');
});

As mentioned by subharb, as from JQuery 3.0 this needs to be changed to:

$('#iframe').on('load', function() {
    alert('frame has (re)loaded ');
});

https://jquery.com/upgrade-guide/3.0/#breaking-change-load-unload-and-error-removed

If you have no control over the page and wish to watch for some kind of change then the modern method is to use MutationObserver

An example of its use, watching for the src attribute to change of an iframe

new MutationObserver(function(mutations) {_x000D_
  mutations.some(function(mutation) {_x000D_
    if (mutation.type === 'attributes' && mutation.attributeName === 'src') {_x000D_
      console.log(mutation);_x000D_
      console.log('Old src: ', mutation.oldValue);_x000D_
      console.log('New src: ', mutation.target.src);_x000D_
      return true;_x000D_
    }_x000D_
_x000D_
    return false;_x000D_
  });_x000D_
}).observe(document.body, {_x000D_
  attributes: true,_x000D_
  attributeFilter: ['src'],_x000D_
  attributeOldValue: true,_x000D_
  characterData: false,_x000D_
  characterDataOldValue: false,_x000D_
  childList: false,_x000D_
  subtree: true_x000D_
});_x000D_
_x000D_
setTimeout(function() {_x000D_
  document.getElementsByTagName('iframe')[0].src = 'http://jsfiddle.net/';_x000D_
}, 3000);

<iframe src="http://www.google.com"></iframe>

Output after 3 seconds

MutationRecord {oldValue: "http://www.google.com", attributeNamespace: null, attributeName: "src", nextSibling: null, previousSibling: null…}
Old src:  http://www.google.com
New src:  http://jsfiddle.net/ 

On jsFiddle

Posted answer here as original question was closed as a duplicate of this one.

Note: The snippet would only work if the iframe is with the same origin.

Other answers proposed the load event, but it fires after the new page in the iframe is loaded. You might need to be notified immediately after the URL changes, not after the new page is loaded.

Here's a plain JavaScript solution:

function iframeURLChange(iframe, callback) {_x000D_
    var unloadHandler = function () {_x000D_
        // Timeout needed because the URL changes immediately after_x000D_
        // the `unload` event is dispatched._x000D_
        setTimeout(function () {_x000D_
            callback(iframe.contentWindow.location.href);_x000D_
        }, 0);_x000D_
    };_x000D_
_x000D_
    function attachUnload() {_x000D_
        // Remove the unloadHandler in case it was already attached._x000D_
        // Otherwise, the change will be dispatched twice._x000D_
        iframe.contentWindow.removeEventListener("unload", unloadHandler);_x000D_
        iframe.contentWindow.addEventListener("unload", unloadHandler);_x000D_
    }_x000D_
_x000D_
    iframe.addEventListener("load", attachUnload);_x000D_
    attachUnload();_x000D_
}_x000D_
_x000D_
iframeURLChange(document.getElementById("mainframe"), function (newURL) {_x000D_
    console.log("URL changed:", newURL);_x000D_
});

<iframe id="mainframe" src=""></iframe>

This will successfully track the src attribute changes, as well as any URL changes made from within the iframe itself.

Tested in all modern browsers.

I made a gist with this code as well. You can check my other answer too. It goes a bit in-depth into how this works.