Sum an Array of Numbers with JavaScript

By  on  

It's rare that I'm disappointed by the JavaScript language not having a function that I need. One such case was summing an array of numbers -- I was expecting Math.sum or a likewise, baked in API. Fear not -- summing an array of numbers is easy using Array.prototype.reduce!

const numbers = [1, 2, 3, 4];
const sum = numbers.reduce((a, b) => a + b, 0);

The 0 represents the starting value while with a and b, one represents the running total with the other representing the value to be added. You'll also note that using reduce prevents side effects! I'd still prefer something like Math.sum(...numbers) but a simple reduce will do!

Recent Features

Incredible Demos

  • By
    Facebook-Style Modal Box Using MooTools

    In my oh-so-humble opinion, Facebook's Modal box is the best modal box around. It's lightweight, subtle, and very stylish. I've taken Facebook's imagery and CSS and combined it with MooTools' awesome functionality to duplicate the effect. The Imagery Facebook uses a funky sprite for their modal...

  • By
    Multiple Background CSS Animations

    CSS background animation has been a hot topic for a long time, mostly because they look pretty sweet and don't require additional elements.  I was recently asked if it was possible to have multiple background animations on a given element and the answer is yes...with...

Discussion

  1. Chris Zuber

    Initializing with 0 might not be necessary since it takes the value from the first item in the array if not provided (and then skips the first item for the rest). It’s very slightly slower to set it to 0.

    Here’s what I wonder though… Suppose this were in some math.js module. Would it be sum(nums) or sum(...nums)? sum([1,2,3]) or sum(1,2,3)? I kinda prefer the latter.

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!