throwIf() function

述語関数が true を返す場合、errの戻り値をスローします。

デフォルトのスロー関数はidentityです。

Signature:

declare function throwIf<T, N extends T>(
  predicate: (input: T) => input is N,
  err?: (input: N) => unknown,
): (input: T) => Exclude<T, N>;

Example

pipe(
  fn(), // return type is string | undefined

  throwIf(isUndefined, (err) => Error("return of fn() is undefined")),
  // err is undefined, and it is return of fn

  (input) => input, // input is string
);

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