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
    Style Textarea Resizers

    Modern browsers are nice in that they allow you to style some odd properties.  Heck, one of the most popular posts on this blog is HTML5 Placeholder Styling with CSS, a tiny but useful task.  Did you know you can also restyle the textarea resizer in WebKit...

  • By
    Creating Spacers with Flexbox

    I was one of the biggest fans of flexbox before it hit but, due to being shuffled around at Mozilla, I never had the chance to use it in any practice project; thus, flexbox still seems like a bit of a mystery to me.  This greatly...

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!