When comparing Crafty.js vs MelonJS, the Slant community recommends Crafty.js for most people. In the question“What are the best HTML5/JavaScript frameworks for web-based games?” Crafty.js is ranked 4th while MelonJS is ranked 7th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Javascript

Pro Eventbinding
Easy to learn, based on Entities and Components, the later being class-like objects that entities inherit.
Pro Modular
Has open function binding systems, allowing easy creation of custom components.
Pro Good support
Devs help resolve issues in a timely manner and are friendly throughout the process.
Pro Tiled support
Natively integrates Tiled map editor. Tiled is a free, open-source map editor that supports orthogonal, isometric and staggered maps.
Pro Good docs
The documentation is intuitively structured and comprehensive allowing you to quickly find information about the engine.
Pro Has tutorials to help you get started
To understand basics of MelonJS, the developers maintain 2 tutorials that are available on the site.
Pro Javascript (and webGL support in latest version)
Cons
Con No IDE
If you like having some huge GUI akin to Gamemaker, Unreal, Unity, etc, Crafty is not for you.
Con API breaks all the time
API breaks are common between version changes.
