Javascript – What’s the fastest way to loop through an array in JavaScript


I learned from books that you should write for loop like this:

for(var i=0, len=arr.length; i < len; i++){
    // blah blah

so the arr.length will not be calculated each time.

Others say that the compiler will do some optimization to this, so you can just write:

for(var i=0; i < arr.length; i++){
    // blah blah

I just want to know which is the best way in practice?

Best Solution

After performing this test with most modern browsers:

Currently, the fastest form of loop (and in my opinion the most syntactically obvious).

A standard for-loop with length caching

    var i = 0, len = myArray.length;
    while (i < len) {
        // your code

I would say, this is definitely a case where I applaud JavaScript engine developers. A runtime should be optimized for clarity, not cleverness.