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
    Camera and Video Control with HTML5

    Client-side APIs on mobile and desktop devices are quickly providing the same APIs.  Of course our mobile devices got access to some of these APIs first, but those APIs are slowly making their way to the desktop.  One of those APIs is the getUserMedia API...

  • By
    MooTools: Set Style Per Media

    I'd bet one of the most used MooTools methods is the setStyle() method, which allows you to set CSS style declarations for an element. One of the limitations of MooTools' setStyle() method is that it sets the specific style for all medias.

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!