One think I struggled a lot with until I got it is that the TypeScript types and the JavaScript code live in totally separate universes, and you cannot cross from the type world to JavaScript values because the types are erased when transpilling - meaning they can't leave any trace.

This means that it's impossible to write this function:

    function isStringType<T>(): boolean { return ... }

    const IS_STRING: boolean = isStringType<string>();

At best you can do something like this, which is inconvenient for more complex cases:

    function isStringType<T, IsString extends boolean = T extends string ? true : false>(isString: IsString): boolean { return isString }

    const IS_STRING_1: boolean = isStringType<string>(true); // compiles
    const IS_STRING_2: boolean = isStringType<string>(false); // type error

You basically need to pass the actual result that you want in and just get a type error if you pass in the wrong one. Still better than nothing.

Link if you want to play with it online: https://www.typescriptlang.org/play?#code/GYVwdgxgLglg9mABDA...

Put another way, you can't do reflection with TypeScript.

You can write that function in C++ templates, and I naively assumed that it's possible in TypeScript too, since from my observations TypeScript allows complex typing to be expressed easier in general than C++.