[removed] hiding prototype methods in for loop?

Question

So lets say I\'ve added some prototype methods to the Array class:

Array.prototype.containsKey = function(obj) {
    for(var key in this)
        if (key =         


        

Answer 1

For high-performance iteration over JavaScript arrays, use either a for or while loop. Nicholas Zakas discusses the most-performant options for iterating over arrays in his Tech Talk Speed Up Your JavaScript.

Your best bet is probably something like this:

for (var i = collection.length - 1; i >= 0; i--) {
  if (obj == collection[i]) return true;
}

This approach will be peform best for a few reasons:

• Only a single local variable is allocated
• The collection's length property is only accessed once, at the initialization of the loop
• Each iteration, a local is compared to a constant (i >= 0) instead of to another variable