Fastest JavaScript summation

Question

What is the fastest way to sum up an array in JavaScript? A quick search turns over a few different methods, but I would like a native solution if possible. This will run under SpiderMonkey.

Thinking very inside-the-box I have been using:

var count = 0;
for(var i = 0; i < array.length; i++)
{
    count = count + array[i];
}

I'm sure there is a better way then straight iteration.

Answer 1

You should be able to use reduce.

var sum = array.reduce(function(pv, cv) { return pv + cv; }, 0);

Source

Answer 2

The fastest loop, according to this test is a while loop in reverse

var i = arr.length; while (i--) { }

So, this code might be the fastest you can get

Array.prototype.sum = function () {
    var total = 0;
    var i = arr.length; 

    while (i--) {
        total += this[i];
    }

    return total;
}

Array.prototype.sum adds a sum method to the array class... you could easily make it a helper function instead.

Answer 3

Improvements

Your looping structure could be made faster:

---

   var count = 0;
   for(var i=0, n=array.length; i < n; i++) 
   { 
      count += array[i]; 
   }

This retrieves array.length once, rather than with each iteration. The optimization is made by caching the value.

If you really want to speed it up:

---

   var count=0;
   for (var i=array.length; i--;) {
     count+=array[i];
   }

This is equivalent to a while reverse loop. It caches the value and is compared to 0, thus faster iteration.

For a more complete comparison list, see my JSFiddle.
Note: array.reduce is horrible there, but in Firebug Console it is fastest.

Answer 4

For your specific case, just use the reduce method of Arrays:

var sumArray = function() {
    // Use one adding function rather than create a new one each
    // time sumArray is called
    function add(a, b) {
        return a + b;
    }

    return function(arr) {
        return arr.reduce(add);
    };
}();

alert( sumArray([2, 3, 4]) );