Is TypeScript really a superset of JavaScript?

Question

I just started using TypeScript and sometimes get compiler errors \"use of undeclared variable\". For example the following works in plain JavaScript :

var f         


        

Answer 1

The reason for TypeScript's existence is to have a compiler and language which can enforce types better than vanilla Javascript does. Any regular Javascript is valid TypeScript, syntactically. That does not mean that the compiler must be entirely happy with it. Vanilla Javascript often contains code which is problematic in terms of type security. That doesn't make it invalid TypeScript code, but it's exactly the reason why TypeScript exists and it's exactly the compiler's job to point out those problems to you.

The languages as such are still sub/supersets of one another.