mapOrThrow

mapOrThrow(map, key, transform)

Transforms the value at key in map using transform, throwing an error if the key doesn't exist.

data-first

mapOrThrow(
    new Map([
        ["a", 1],
        ["b", 2],
    ]),
    "a",
    (value) => value * 2,
); // Map(2) { "a" => 2, "b" => 2 }

mapOrThrow(
    new Map([
        ["a", 1],
        ["b", 2],
    ]),
    "c",
    (value) => value * 2,
); // throws FnError

data-last

pipe(
    new Map([
        ["a", 1],
        ["b", 2],
    ]),
    mapOrThrow("a", (value) => value * 2),
); // Map(2) { "a" => 2, "b" => 2 }

pipe(
    new Map([
        ["a", 1],
        ["b", 2],
    ]),
    mapOrThrow("c", (value) => value * 2),
); // throws FnError