[the_gipsy]

For what it's worth, Elm does the runtime checks by means of forcing you to write "de/encoders" that must match the types.

[smt88]

So does TypeScript if you have strict settings. Your input data will be untyped and you will be forced to determine its type before you use it.

[the_gipsy]

TypeScript does nothing like that with any strict settings, because it doesn't provide any JSON parsing alternative, so that is always unsafe.

I bet there are runtime checkers that use some kind of reflection, that would be the next best thing. But I also bet that those force you to annotate/decorate everything.

[hermanradtke]

I do not know of a way to make this a compiler error:

    const user: User = JSON.parse(…);

[dhucerbin]

You can redefine all definitions from lib.d.ts and similar. In my projects, parse function returns unknown, so I need to parse/validate/decode it in runtime to satisfy types.