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

JSLitmus is a lightweight tool for creating ad-hoc JavaScript benchmark tests

Let examine the performance between function expression and function constructor:

What I did above is create a function expression and function constructor performing same operation. The result is as follows:

FireFox Performance Result

IE Performance Result