JuniorTheoryCommon

Which type does TypeScript infer for `shown`?

TypeScript

function label(city: string | null) {
    const shown = city ?? "—";
    return shown;
}

console.log(label(null));

string

Expecting string | null: ?? replaces null and undefined with its right side, and the compiler follows it, so null drops out of the type.
Expecting the literal type "—" because of const: shown may hold any string from city, and string | "—" is the same as string.

What type does city?.toUpperCase() have in this function, and why?
How does city ?? "—" differ from city || "—" when city is an empty string?

JuniorTheoryCommon

TypeScript

function label(city: string | null) {
    const shown = city ?? "—";
    return shown;
}

console.log(label(null));

string

Expecting string | null: ?? replaces null and undefined with its right side, and the compiler follows it, so null drops out of the type.
Expecting the literal type "—" because of const: shown may hold any string from city, and string | "—" is the same as string.

What type does city?.toUpperCase() have in this function, and why?
How does city ?? "—" differ from city || "—" when city is an empty string?

Which type does TypeScript infer for shown?