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copied!<p>The "Script error." happens in Firefox, Safari, and Chrome when an exception violates the browser's <a href="http://en.wikipedia.org/wiki/Same_origin_policy" rel="noreferrer">same-origin policy</a> - i.e. when the error occurs in a script that's hosted on a domain other than the domain of the current page.</p> <p>This behavior is intentional, to prevent scripts from leaking information to external domains. For an example of why this is necessary, imagine accidentally visiting <code>evilsite.com</code>, that serves up a page with <code><script src="yourbank.com/index.html"></code>. (yes, we're pointing that script tag at html, not JS). This will result in a script error, but the error is interesting because it can tell us if you're logged in or not. If you're logged in, the error might be <code>'Welcome Fred...' is undefined</code>, whereas if you're not it might be <code>'Please Login ...' is undefined</code>. Something along those lines.</p> <p>If evilsite.com does this for the top 20 or so bank institutions, they'd have a pretty good idea of which banking sites you visit, and could provide a much more targeted phishing page. (This is just one example, of course. But it illustrates why browsers shouldn't allow <em>any</em> data to cross domain boundaries.)</p> <p>I've tested this in the latest versions of Safari, Chrome, and Firefox - they all do this. IE9 does not - it treats x-origin exceptions the same as same-origin ones. (And Opera doesn't support onerror.)</p> <p>From the horses mouth: <a href="http://trac.webkit.org/browser/branches/chromium/648/Source/WebCore/dom/ScriptExecutionContext.cpp?rev=77122#L301" rel="noreferrer">WebKit source that checks origin</a> when passing exceptions to onerror(). And the <a href="https://dxr.mozilla.org/mozilla-beta/source/dom/base/nsJSEnvironment.cpp#464" rel="noreferrer">Firefox source that checks</a>.</p> <p><strong>UPDATE (10/21/11)</strong>: The <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=363897" rel="noreferrer">Firefox bug that tracks this issue</a> includes a link to the blog post that inspired this behavior. </p> <p><strong>UPDATE (12/2/14)</strong>: You can now enable full cross-domain error reporting on some browsers by specifying a <a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script#attr-crossorigin" rel="noreferrer"><code>crossorigin</code> attribute</a> on script tags and having the server send the appropriate <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS" rel="noreferrer">CORS</a> HTTP response headers.</p>

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