They don't increase i at all. It is impossible to count to 10,000 at a rate of 200Mhz. That implies a 2000Ghz processor. JS Perf is fundamentally broken. It

They don't increase i at all. It is impossible to count to 10,000 at a rate of 200Mhz. That implies a 2000Ghz processor. JS Perf is fundamentally broken. It doesn't force a side effect, and from the debugger, the first step it does is something like: while(100,000,000--) { // your code here } The chrome compiler then recognizes the loops can be swapped, and eliminated, thus it runs your code once, yet jsperf thinks it ran it hundreds of millions of times.