when() function

最初の引数の条件に基づいて元の値、または 2 番目の引数として渡された関数の実行結果を返します。

Signature:

declare function when<T, S extends T, R>(
  predicate: (input: T) => input is S,
  callback: (input: S) => R,
): (a: T) => R | Exclude<T, S>;

Example

when(
  isNumber,
  () => `This is number`
  100,
); // This is number

with pipe

pipe(
  100,
  when(isNumber, () => `This is number`),
); // This is number

pipe(
  100,
  when(isNumber, (value) => value * 2),
); // 200

pipe(
  100,
  when(
    isString,
    () => `This is number`, // not work
  ),
); // 100

Open Source Code