Type Conversion with JavaScript Arrays

By  on  

JavaScript's loose nature allows developers to employ amazing tricks to do just about anything you'd like. I've detailed how you can filter falsy values in arrays using a filter(Boolean) trick, but reader David Hibshman shared another trick for typecasting array values the same way.

To typecast an array of elements, you can use map and the desired return type:

["1", "9", "-9", "0.003", "yes"].map(Number);
// [1, 9, -9, 0.003, NaN]

I love this trick but you could argue the code itself could be considered confusing, so wrapping it a helper function would be helpful:

function arrToNumber(arr) {
  return arr.map(Number).filter(Boolean);
}

Validation could and should probably be more rigorous but basic validation through typecasting might help you!

Recent Features

  • By
    7 Essential JavaScript Functions

    I remember the early days of JavaScript where you needed a simple function for just about everything because the browser vendors implemented features differently, and not just edge features, basic features, like addEventListener and attachEvent.  Times have changed but there are still a few functions each developer should...

  • By
    Vibration API

    Many of the new APIs provided to us by browser vendors are more targeted toward the mobile user than the desktop user.  One of those simple APIs the Vibration API.  The Vibration API allows developers to direct the device, using JavaScript, to vibrate in...

Incredible Demos

  • By
    PHP Woot Checker – Tech, Wine, and Shirt Woot

    If you haven't heard of Woot.com, you've been living under a rock. For those who have been under the proverbial rock, here's the plot: Every day, Woot sells one product. Once the item is sold out, no more items are available for purchase. You don't know how many...

  • By
    Vertically Centering with Flexbox

    Vertically centering sibling child contents is a task we've long needed on the web but has always seemed way more difficult than it should be.  We initially used tables to accomplish the task, then moved on to CSS and JavaScript tricks because table layout was horribly...

Discussion

  1. jzrskc
    ["0", "9", "-9", "0.003", "yes", true, false, undefined, null].map(Number);
    // [0, 9, -9, 0.003, NaN, 1, 0, NaN, 0]
    
    ["0", "9", "-9", "0.003", "yes", true, false, undefined, null].map(parseFloat)
    // [0, 9, -9, 0.003, NaN, NaN, NaN, NaN, NaN]
    
  2. MKM

    The .filter(Boolean) part also sees the zeros as booleans and removes those numbers.

  3. BryanYang

    very useful!

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