It's a character after the closing curly brace:
I copy-pasted your code in Firefox' console, postfixed with a undefined method invocation:
'function changeColumnWidth() {
var w = Math.random() * 200+80;
$('#menu').css("width", w+"px");
}?'.l(); /* .l() triggers a TypeError, since it's not defined */
A TypeError (undefined) shows up, which includes the parsed (escaped) code:
TypeError: "function changeColumnWidth() { var w = Math.random() * 200+80; $('#menu').css("width", w+"px");}u200B".l is not a function
.
^^^^^^ Here's the error.
Now, the troublemaker is found. To fix it, open your code in a text editor, and remove the invisible character. This character can be detected by walking through all characters using the arrow keys.
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