When comparing Amber vs Blocks.js, the Slant community recommends Blocks.js for most people. In the question“What are the best JavaScript libraries for building a UI?” Blocks.js is ranked 10th while Amber is ranked 19th. The most important reason people chose Blocks.js is:
Blocks.js is just 16.5KB minified and gzipped. So it's pretty small.
Specs
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Pros
Pro Includes an IDE
Amber includes an integrated development environment with a class browser, workspace, transcript, object inspector and debugger.
Pro Smalltalk is a simple, elegant, and powerful language
Pro One-to-one JS equivalent
Amber is written in itself, including the parser and compiler, and compiles into efficient JavaScript, mapping one-to-one with the JS equivalent.
Pro Small footprint
Blocks.js is just 16.5KB minified and gzipped. So it's pretty small.
Pro Modular structure
Apps developed with blocks.js are modular in structure and make use of reusable objects. This makes these applications very maintainable.
Cons
Con Very few learning resources
There are very little learning resources for Amber outside the official documentation. Which may not be enough for beginners, especially people that don't have much experience in programming.
Con Relatively new
Blocks.js is a relatively new library. It doesn't have much support and there re not many people who use it. So if you run into any problems it would be hard to get solutions.