How to block external hyperlinks in an iframed page?

Question

I'm making a website that shows another website in an iframe (cross-domain). The problem is that there are external hyperlinks in the site in the iframe, and I want to somehow block or disable them. I want to block ONLY external hyperlinks.

That is, if the iframed page is example.com/info:

• Block: <a href="http://other_example.net/pwn">Bad Link</a>
• Allow: <a href="http://example.com/donate">Good Link</a>

How can I do this? Greasemonkey and some kind of script? Or something else?

Answer 1

Either a userscript or a browser extension can do this. A Greasemonkey script will run on a page, irregardless of whether it's in an iframe (unless you tell it not to).
To block external links, compare each link's hostname to the iframed page's hostname.

Here's a complete Greasemonkey script that illustrates the process:

// ==UserScript==
// @name     _Block cross-domain links
// @include  http://www.puppylinux.com/*
// @grant    GM_addStyle
// ==/UserScript==

//-- Only run if the page is inside a frame or iframe:
if (window.top !== window.self) {
    var linkList = document.querySelectorAll ("a");

    Array.prototype.forEach.call (linkList, function (link) {
        if (link.hostname !== location.hostname) {
            //-- Block the link
            link.href = "javascript:void(0)";
        }
    } );

    //-- Mark the links, so the user knows what's up.
    GM_addStyle ( "                             \
        a[href='javascript:void(0)'] {          \
            white-space: nowrap;                \
            cursor: default;                    \
        }                                       \
        a[href='javascript:void(0)']::after {   \
            background: orange;                 \
            content: 'X';                       \
            display: inline-block;              \
            margin-left: 0.3ex;                 \
            padding: 0 0.5ex;                   \
        }                                       \
    " );
}

You can install and run that script against this test page on jsFiddle.

Note:

• The containing page is fiddle.jshell.net/9aQv5/3/show/.
• The iframed page is www.puppylinux.com.
• When you run that script, external links are disabled and the disabled links are marked with an "X".
• This approach is for simple static pages. For AJAX driven pages, use waitForKeyElements().

Answer 2

For this you have to compare your url href attribute using Javascript function as below

// this function will give host name
function get_hostname(url) {
    var m = url.match(/^http:\/\/[^/]+/);
    return m ? m[0] : null;
}

   var hostName =  get_hostname("http://example.com/path");

This will return http://example.com/ as in your example output.

Using above function you can compare your URL and if its going to mathch with your host name - then you can allow to redirect the page or else you can show message for external Links