How do you performance test JavaScript code?

Question

CPU Cycles, Memory Usage, Execution Time, etc.?

Added: Is there a quantitative way of testing performance in JavaScript besides just perception of how fast the code

Answer 1

Here is a simple function that displays the execution time of a passed in function:

var perf = function(testName, fn) {
    var startTime = new Date().getTime();
    fn();
    var endTime = new Date().getTime();
    console.log(testName + ": " + (endTime - startTime) + "ms");
}