this post was submitted on 08 Oct 2023
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Programming
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No, it doesn't fail. It compiles to perfectly valid JS that runs exactly as you'd expect. The type checking itself errors, because you've made an error - but the compilation isn't prevented by this error.
So yes, Typescript is a superset of JavaScript.
That is an important difference. Still lots of people, myself included, classify "compiler printing an error (not a warning)" as failure, even if bizzarly the code still runs somehow.
That's because you're missing the distinction between compiler and type checker. The compiler doesn't check types, it strips them. The type checker only checks types, it doesn't compile. They are often used in conjunction, though increasingly the compilation is done by e.g. esbuild.
But there is nothing "bizarre" about the code running, since literally, TS is a superset of JS.
Wouldn't it fail in strict mode?
The type checking does, but not the compilation.