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

And with arrow functions introduced in ES6, it's even simpler:

sum = array.reduce((pv, cv) => pv + cv, 0); 

Answer 2

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.

---

Compare Structures

I started a JSPerf for array summations. It was quickly constructed and not guaranteed to be complete or accurate, but that's what edit is for :)

Answer 3

While searching for the best method to sum an array, I wrote a performance test.

In Chrome, "reduce" seems to be vastly superior

I hope this helps

// Performance test, sum of an array
  var array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
  var result = 0;
// Eval
  console.time("eval");
  for(var i = 0; i < 10000; i++) eval("result = (" + array.join("+") + ")");
  console.timeEnd("eval");
// Loop
  console.time("loop");
  for(var i = 0; i < 10000; i++){
    result = 0;
    for(var j = 0; j < array.length; j++){
      result += parseInt(array[j]);
    }
  }
  console.timeEnd("loop");
// Reduce
  console.time("reduce");
  for(var i = 0; i < 10000; i++) result = array.reduce(function(pv, cv) { return pv + parseInt(cv); }, 0);
  console.timeEnd("reduce");
// While
  console.time("while");
  for(var i = 0; i < 10000; i++){
    j = array.length;
    result = 0;
    while(j--) result += array[i];
  }
  console.timeEnd("while");

eval: 5233.000ms

loop: 255.000ms

reduce: 70.000ms

while: 214.000ms