Timed Process Array

timedProcessArray.js

// timedProcessArray

// Since each new Date object is initialized with the current system time, you can time
// code by creating new Date objects periodically and comparing their values. The plus
// operator (+) converts the Date object into a numeric representation so that any further
// arithmetic doesn’t involve conversions. This same basic technique can be used to op-
// timize the previous timer patterns.

function timedProcessArray(items, process, callback){
    var todo = items.concat();   //create a clone of the original
    setTimeout(function(){
        var start = +new Date();
        do {
             process(todo.shift());
        } while (todo.length > 0 && (+new Date() - start < 50));
        if (todo.length > 0){
            setTimeout(arguments.callee, 25);
        } else {
            callback(items);
        }
    }, 25);
}

// The addition of a do-while loop in this function enables checking the time after each
// item is processed. The array will always contain at least one item when the timer func-
// tion executes, so a post-test loop makes more sense than a pretest one. When run in
// Firefox 3, this function processes an array of 1,000 items, where process() is an empty
// function, in 38–43 milliseconds; the original processArray() function processes the
// same array in over 25,000 milliseconds. This is the power of timing tasks before break-
// ing them up into smaller chunks.