What is the type assertion operator for in TypeScript?

Question

The spec doesn\'t say much about where the type assertion operator might be helpful in TypeScript. I didn\'t need it in my code. So I am curious what sort of problems it is

Answer 1

There are two forms of Typescript type assertions. Examples from the Typescript handbook here.

1. Angle bracket syntax for type assertions (doesn't work within a tsx file):

let strLength: number = (someValue).length;

2. as syntax for type assertions (works within ts or tsx alike):

let strLength: number = (someValue as string).length;

Type assertions override the (limited) type inference capabilities of the ever current version of Typescript, which can be a good thing if you are correct, but there is also a risk that your judgment is incorrect and TS will believe you. If there's a likely mismatch between what you infer and what TS infers, TS will still balk, then you can more strongly overrule the TS inference by as unknown as string.