Profile JS operations easily! This function tells you the median number of times an operation will run per second, based on five separate counts. Pass it a name for the test and an operation to perform. Based on an idea in Raphaele Cecco's "Supercharged HTML Graphics", which in turn was inspired by code by John Resig.

profile.js

/*
 * @param: name - String, a label for the test - usually the function's name
 * @param: operation - Function, the code to test
 */
var profile = function ( name, operation ) {
	var iterate = function ( operation ) { 
		var start = new Date().getTime();
		var elapsed = 0;

		for( var itrs = 0; elapsed < 1000; itrs++ ) {
			operation();
			elapsed = new Date().getTime() - start;
		}

		return itrs;
	}

	var results = [];

	// run five sets of tests
	for( var i = 5; i >= 0; i-- ){
		results.push( iterate( operation ) );
	}

	results.sort();

	console.warn( name +' ran a median of '+ results[2] +' times.' );
}

test.js

// declaratively decide which of three paths to run in response to a passed value
var declarative = function ( value ) {
	switch( value ) {
	case 0: case 1:
		doTheRightThing( value );
		break;
	case 2: case 3: case 4: case 5: case 6: case 7: case 8: case 9:
		doTheOtherThing( value );
		break;
	default:
		doTheDefaultThing( value );
	}
}

// logically decide which of three paths to run in response to a passed value
var logical = function ( value ) {
	if( value <= 1 ) {
		doTheRightThing(  value );
	} else if ( value >= 2 && value <= 9 ) {
		doTheOtherThing( value );
	} else {
		doTheDefaultThing( value );
	}
}

// the three different responses
var doTheRightThing = function ( data )   { console.log('Right:', data ); }
var doTheOtherThing = function ( data )   { console.log('Other:', data ); }
var doTheDefaultThing = function ( data ) { console.log('Default:', data ); }

// repeat one of the above function over a data set (the numbers 19 -> 0)
var repeat20 = function ( fn ) {
	for( var count = 19; count >= 0; count-- ){
		fn( count );
	}
}

// call profile from the other gist item, with a name, and a function to run the iterator
profile( 'declarative', function () { repeat20( declarative )} );
profile( 'logical', function () { repeat20( logical )} );