I'm not a huge fan of TypeScript (though I will admit that it's way more useful than CoffeeScript). My main issues with it are that: 1. The type definition file

I'm not a huge fan of TypeScript (though I will admit that it's way more useful than CoffeeScript). My main issues with it are that: 1. The type definition files tend to get out of date. 2. The build step is time consuming for large apps. 3. It adds complexity to your app and opens it up to new kinds of errors (particularly during setup, different typescript versions...). I prefer using plain JavaScript - When I need to find a definition for a function, I just do a text search for it in my IDE. Text search isn't as nice as intellisense for beginners but you get used to it pretty quickly and it's actually pretty efficient once you do. I also like to read through the code a bit before using a function written by someone else, I find that just knowing the interface is often not enough - Often you want to know how specific edge cases are handled and it encourages you to fix bugs in other people's code instead of thinking "This class doesn't work, it's not my problem - I'll just hack a solution to work around it".