Easily add an array of values in Javascript (eg. without loops)

Question

I was wondering if anyone knows of a nice way of adding an array of values in javascript?

I came up with:

var myArray = [1,2,3,4,5];
var total = eval(myArray.join("+"));

Which is nice and short, but I'm guessing going from num to string and then evaling to get back to a number is a slow way of getting the total.

• El Ronnoco: Yep I'd say that's definitely inefficient!
• user395760: Why would you avoid loops? Much less use eval for this?
• Andy E: eval is evil. Didn't you get the memo?
• Mohammad Usman: Possible duplicate of How to find the sum of an array of numbers

Answer 1

The most appropriate method of doing this is to use the [Array.prototype.reduce]( https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/reduce) function, an addition to the language in ECMAScript 5th Edition:

var myArray = [1,2,3,4,5],
 total = myArray.reduce(function (curr, prev) { return curr + prev; });
alert(total);

Of course, this isn't supported in older browsers so you might want to include the compatibility implementation in your code.

• El Ronnoco: Would this execute faster than protoype.sum function in my answer? This isn't a criticism btw I was not aware of the reduce function and it looks very useful but I would think that for something as simple as summing perhaps the sum would run faster?
• David: Thanks, this is what I was looking for, I googled but didn't think to look on MDN.
• user395760: @El Ronnoco: It would propably run slightly faster, but not even noticeable unless the array is really huge. What really bugs me about this solution is the verbose lambda needed for summing... operator sections are awesome (sum = reduce (+) anyone?).
• Andy E: @El: I would expect the native reduce to run faster, but not the compatibility implementation.
• El Ronnoco: @delnan when you say 'it would run slightly faster' do you mean the reduce or the custom protoype?

Answer 2

UPDATE - To combine Andy's method and the Prototyping method...

Array.prototype.sum = function(){
 return this.reduce(function(a,b) {return a+b} );
}

Now all array will have the sum method. eg var total = myArray.sum();.

Original answer...

I'd be tempted with just

var myArray = [1,2,3,4,5];
var sum = 0;
for (var i=0, iMax=myArray.length; i < iMax; i++){
 sum += myArray[i];
};
alert(sum);

break it out into a function if you're using it a lot. Or even neater, prototype it...

Array.prototype.sum = function(){
 for(var i=0, sum=0, max=this.length; i < max; sum += this[i++]);
 return sum; 
}
var myArray = [1,2,3,4,5];
alert(myArray.sum());

Courtesy of DZone Snippets

• user395760: Please format properly. If the code seems to convulted, dropping formatting (in particular whitespace) is not an acceptable response.
• El Ronnoco: @delnan I'm sorry, what exactly are you referring to?
• El Ronnoco: @delnan - Do you mean the for loop formatting - if so, I have fixed it :)
• user395760: @El Ronnoco: (Edit: Yes, although it could still be improved IMHO ;)) The loops. In about every sensible coding style, it would include two or three line breaks and spaces around operators.
• El Ronnoco: @delnan I think the spaces round operators debate it ongoing :) Neither style offends my eye particularly.