Chrome userscript error: “Unsafe JavaScript attempt to access frame”

// the iframe of the div I need to access
var iframe = document.getElementsByTagName("iframe")[2];
var innerDoc = iframe.contentDocument || iframe.contentWindow.document;

// resize 'player' in the iframe
innerDoc.getElementById('player').width = "1000px";
innerDoc.getElementById('player').height = "650px";

Running in a userscript for this url:

Why does Chrome come out with this error and fail the script?:

Unsafe JavaScript attempt to access frame with URL 
from frame with URL 
Domains, protocols and ports must match.

(I'm only a basic Javascript user)

Final code, many thanks to the answerer:

// ==UserScript==
// @name       Resize
// @include*
// @include*
// ==/UserScript==

if (!( === window.self)) {
    var player = document.getElementById('player');

function setSize(player) {"width", "1000px");"height", "650px");



It's true that ordinary javascript cannot access iframe content, that's on a different domain, for security reasons. However, this by no means stops userscripts in Chrome, Tampermonkey or Greasemonkey.

You can process iframed content in a userscript because Chrome (and Firefox) process iframe'd pages just as if they were the main page. Accounting for that, scripting such pages is a snap.

For example, suppose you have this page at

    <iframe src=""></iframe>

If you set your @match directives like this:

// @match*
// @match*

Then your script will run twice -- once on the main page and once on the iframe as though it were a standalone page.

So if your script was like this:

// ==UserScript==
// @name  _Test iFrame processing in Chrome and Tampermonkey
// @match*
// @match*
// ==/UserScript==

if (/domain_A\.com/i.test (document.location.href) ) {
    //Main page ("background", "lime", "important");
else {
    //iFrame ("background", "pink", "important");

You would see the main page in lime-green, and the iframed page in pink.

Alternatively, you can test like this:

if ( === window.self) {
    //--- Code to run when page is the main site...
else {
    //--- Code to run when page is in an iframe...

As you discovered (per comment on another answer), you can disable the same origin policy on Chrome. Don't do this! You will leave yourself open to all kinds of shenanigans set up by bad people. In addition to evil sites, many nominally "good" sites -- that allow users to post content -- could potentially track, hack, or spoof you.


For security reasons your browser won't allow you to access javascript in an iframe from another domain.

See the top answer here:

jQuery cross domain iframe scripting


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