JavaScript.com - A free resource for learning and developing in JavaScript

UserTesting.com - Usability testing has never been easier. Get videos of real people speaking their thoughts as they use websites, mobile apps, prototypes and more!

BundlePhobia - Find the performance impact of adding a npm package to your bundle.

Userbrain - Easy, fast, and affordable user testing for websites and prototypes.

JavaScript Quiz - Check your knowledge by having fun.

userinput.io - Get on-demand feedback for your app, website or idea. Learn how to improve by hearing real opinions.