JuniorTheoryCommon

What does tsc report for this program?

TypeScript

type Size = "S" | "M" | "L";

function order(size: Size) {
    console.log(size);
}

let mine = "M";
order(mine);

An error: type string does not fit the parameter type Size

Expecting silence because mine holds "M": let widens its type to string, and string does not fit Size.
Expecting a type check at run time: types are erased, so the JavaScript prints M without any error.

JuniorTheoryCommon

TypeScript

type Size = "S" | "M" | "L";

function order(size: Size) {
    console.log(size);
}

let mine = "M";
order(mine);

An error: type string does not fit the parameter type Size

Expecting silence because mine holds "M": let widens its type to string, and string does not fit Size.
Expecting a type check at run time: types are erased, so the JavaScript prints M without any error.