mapOrElse

mapOrElse(map, key, transform, orElse)

Transforms the value at key in map using transform, calling orElse with the map if the key doesn't exist.

data-first

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

mapOrElse(
    new Map([
        ["a", 1],
        ["b", 2],
    ]),
    "c",
    (value) => value * 2,
    (map) => map.size,
); // 2

data-last

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

pipe(
    new Map([
        ["a", 1],
        ["b", 2],
    ]),
    mapOrElse(
        "c",
        (value) => value * 2,
        (map) => map.size,
    ),
); // 2