Learn JavaScript - Learn JavaScript with guided tests and flashcards
Codacy - Automatically reviews code style, security, duplication, complexity, and coverage on every change while tracking code quality throughout your sprints.
The Ultimate SaaS Quiz - Challenge your friends and improve your SaaS knowledge
SonarQube - SonarQube, a core component of the Sonar solution, is an open source, self-managed tool that systematically helps developers and organizations deliver Clean Code.
JavaScript.com - A free resource for learning and developing in JavaScript
CodeClimate - Code Climate provides automated code review for your apps, letting you fix quality and security issues before they hit production. We check every commit, branch and pull request for changes in quality and potential vulnerabilities.