Summary

Fixes gh-4784

In IE 11 we'd just throw an empty error now, in others - the reported error. We wouldn't include input data in the thrown error anymore.

+10 bytes, although I cheated a bit - I also removed an assignment of xml to undefined in catch as any error would happen before the assignment so the variable would already hold the undefined value. Without this optimization, it'd be +13 bytes.

That +10 can be changed to -3 if we just call:

jQuery.error( parserErrorElem && parserErrorElem.textContent )

but that has two issues. Here's the returned element parsererror (after pretty-printing) in Blink & WebKit:

<parsererror
	xmlns="http://www.w3.org/1999/xhtml"
	style="display: block; white-space: pre; border: 2px solid #c77; padding: 0 1em 0 1em; margin: 1em; background-color: #fdd; color: black">
	<h3>This page contains the following errors:</h3>
	<div style="font-family:monospace;font-size:12px">error on line 14 at column 9: Opening and ending tag mismatch: th line 0 and tr
</div>
	<h3>Below is a rendering of the page up to the first error.</h3>
</parsererror>

and here's the one in Gecko:

<parsererror xmlns="http://www.mozilla.org/newlayout/xml/parsererror.xml">
	XML Parsing Error: mismatched tag. Expected: &lt;/th&gt;.
Location: http://sandbox.l/test.xhtml
Line Number 14, Column 6:
	<sourcetext>			&lt;/tr&gt;\n--------------------------^</sourcetext>
</parsererror>

If we just print textContent, in Chrome the text will miss spaces in some places:

This page contains the following errors:error on line 14 at column 9: Opening and ending tag mismatch: th line 0 and tr
Below is a rendering of the page up to the first error.

That may not be enough a reason to add bytes but here's what ends up in Firefox:

XML Parsing Error: mismatched tag. Expected: </th>.
Location: http://sandbox.l/test.xhtml
Line Number 14, Column 6:			</tr>
--------------------------^

Firefox prints ASCII art which is misaligned now. With the code from this PR, here's what gets printed:

XML Parsing Error: mismatched tag. Expected: </th>.
Location: http://sandbox.l/test.html
Line Number 14, Column 6:
			</tr>
--------------------------^

On the other hand, it actually uses tabs to pad </tr> and the alignment depends on tab being rendered as 8 characters... So maybe we can give up on that.

EDIT: Actually, this will mostly be printed in the DevTools of the respective browser, here: Firefox. So it should show up correctly in the console.

Let's make a decision at the next meeting.

Checklist

• All authors have signed the CLA at https://cla.js.foundation/jquery/jquery
• New tests have been added to show the fix or feature works
• Grunt build and unit tests pass locally with these changes
• If needed, a docs issue/PR was created at https://github.com/jquery/api.jquery.com