JuniorTheoryCommon

Which types does TypeScript infer for `a` and `b`?

TypeScript

function last<T>(xs: T[]): T {
    return xs[xs.length - 1];
}

const a = last([1, 2, 3]);
const b = last(["x", "y"]);
console.log(a, b);

number and string

Expecting T fixed by the first call: inference starts over at each call, so last(["x", "y"]) reads string from its own argument.
Expecting any, as in a function without a type parameter: TypeScript infers T from the argument, so a is a number.

JuniorTheoryCommon

TypeScript

function last<T>(xs: T[]): T {
    return xs[xs.length - 1];
}

const a = last([1, 2, 3]);
const b = last(["x", "y"]);
console.log(a, b);

number and string

Expecting T fixed by the first call: inference starts over at each call, so last(["x", "y"]) reads string from its own argument.
Expecting any, as in a function without a type parameter: TypeScript infers T from the argument, so a is a number.

Which types does TypeScript infer for a and b?