jQuery exception logic flow examples... the "assert" function is being called in a couple places. Most of them are to detect Opera and/or other odd browsers. I highlighted the error lines with "/***************** ERROR ON NEXT LINE ****************/" It seems to me that they should already know if they're running a browser that requires this fea…

gistfile1.js

// jquery 2.0.2 line 1192+
function assert( fn ) {
  var div = document.createElement("div");

	try {
		return !!fn( div );
	} catch (e) {
		return false;
	} finally {
		// Remove from its parent by default
		if ( div.parentNode ) {
			div.parentNode.removeChild( div );
		}
		// release memory in IE
		div = null;
	}
}



// jQuery 2.0.2 line 1549+
  	assert(function( div ) {

			// Support: Opera 10-12/IE8
			// ^= $= *= and empty values
			// Should not select anything
			// Support: Windows 8 Native Apps
			// The type attribute is restricted during .innerHTML assignment
			var input = doc.createElement("input");
			input.setAttribute( "type", "hidden" );
			div.appendChild( input ).setAttribute( "t", "" );

			if ( div.querySelectorAll("[t^='']").length ) {
				rbuggyQSA.push( "[*^$]=" + whitespace + "*(?:''|\"\")" );
			}

			// FF 3.5 - :enabled/:disabled and hidden elements (hidden elements are still enabled)
			// IE8 throws error here and will not see later tests
			if ( !div.querySelectorAll(":enabled").length ) {
				rbuggyQSA.push( ":enabled", ":disabled" );
			}

			// Opera 10-11 does not throw on post-comma invalid pseudos
      /*****************  ERROR ON NEXT LINE ****************/
      // SCRIPT5022: Exception was thrown at line 1571, column 4 in ms-appx://c33865be-41fa-45ec-b8f3-4d25e60ad0f3/Scripts/jquery-2.0.2.js 0x800a139e - JavaScript runtime error: SyntaxError
			div.querySelectorAll("*,:x");
			rbuggyQSA.push(",.*:");
		});
    
    // jquery 2.0.2 line 1581+
      	assert(function( div ) {
			// Check to see if it's possible to do matchesSelector
			// on a disconnected node (IE 9)
			support.disconnectedMatch = matches.call( div, "div" );

			// This should fail with an exception
			// Gecko does not error, returns false instead
      /*****************  ERROR ON NEXT LINE ****************/
      //SCRIPT5022: Exception was thrown at line 1588, column 4 in ms-appx://c33865be-41fa-45ec-b8f3-4d25e60ad0f3/Scripts/jquery-2.0.2.js 0x800a139e - JavaScript runtime error: SyntaxError
			matches.call( div, "[s!='']:x" );  
			rbuggyMatches.push( "!=", pseudos );
		});

I don't see anything wrong here (in this case). Assert should fail with false if the block false or an exception is thrown. They also need to assure a debug statement like assert doesn't have side-affects like adding things to the DOM.

Well, the problem is that using a "break on throw" option in a debugger is REALLY useful.. jQuery is the only thing that does this when the script file is included. It makes us disable the "break on throw" and, thus makes debugging much harder.

Don't break on caught exceptions. We caught it because we expected it.

• https://bugs.jquery.com/ticket/13881
• https://bugs.jquery.com/ticket/14123