Chrome userscript error: "Unsafe JavaScript attempt to access frame"

Question

// 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: http://www.free-tv-video-online.me/player/sockshare.php?id=24DA6EAA2561FD60

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

Unsafe JavaScript attempt to access frame with URL http://www.sockshare.com/embed/24DA6EAA2561FD60 
from frame with URL http://www.free-tv-video-online.me/player/sockshare.php?id=24DA6EAA2561FD60. 
Domains, protocols and ports must match.

(I'm only a basic Javascript user)

Final code, many thanks to the answerer:

// ==UserScript==
// @name       Resize
// @include    http://www.free-tv-video-online.me/player/sockshare.php*
// @include    http://www.sockshare.com/*
// ==/UserScript==

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

function setSize(player) {
    player.style.setProperty("width", "1000px");
    player.style.setProperty("height", "650px");
}

Community · Accepted Answer · 2017-05-23 12:33:02Z

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 domain_A.com:

<html>
<body>
    <iframe src="http://domain_B.com/SomePage.htm"></iframe>
</body>
</html>

If you set your @match directives like this:

// @match http://domain_A.com/*
// @match http://domain_B.com/*

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 http://domain_A.com/*
// @match http://domain_B.com/*
// ==/UserScript==

if (/domain_A\.com/i.test (document.location.href) ) {
    //Main page
    document.body.style.setProperty ("background", "lime", "important");
}
else {
    //iFrame
    document.body.style.setProperty ("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.top === 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.

Oh wow, that worked perfectly. Put my final code in the OP, thank you kindly!

Community · Accepted Answer · 2017-05-23 12:00:49Z

1

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

edited May 23, 2017 at 12:00

CommunityBot

11 silver badge

answered May 19, 2012 at 15:53

Sherms

1,6662 gold badges16 silver badges33 bronze badges

5 Comments

yellow-saint Over a year ago

Oh, I see. I misunderstood the error (and the other explanations for it). You've somehow made it simpler to understand :)

yellow-saint Over a year ago

stackoverflow.com/a/6083677/1053937 - found a way of disabling that security option :)

Sherms Over a year ago

Not expecting your users to do that though are you?

Brock Adams Over a year ago

This answer is not correct for userscripts. They have a mechanism to work around this cross-domain restriction, and without compromising security.

yellow-saint Over a year ago

Rhodesian, as I said it is for a userscript

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