takeWhile

takeWhile() function

Returns Iterable/AsyncIterable that taken values as long as each value satisfies the give f.

Signature:

declare function takeWhile<A, B>(f: (a: A) => B, iterable: Iterable<A>): IterableIterator<A>;

declare function takeWhile<A, B>(f: (a: A) => B, iterable: AsyncIterable<A>): AsyncIterableIterator<A>;

declare function takeWhile<A extends Iterable<unknown> | AsyncIterable<unknown>, B>(f: (a: IterableInfer<A>) => B): (iterable: A) => ReturnIterableIteratorType<A>;

Example

const iter = takeWhile(a => a < 3, [1, 2, 3, 4, 5, 6]);
iter.next() // {done:false, value: 1}
iter.next() // {done:false, value: 2}
iter.next() // {done:true, value: undefined}

// with pipe
pipe(
 [1, 2, 3, 4, 5, 6],
 takeWhile(a => a < 3),
 toArray,
); // [1, 2]

await pipe(
 Promise.resolve([1, 2, 3, 4, 5, 6]),
 takeWhile(a => a < 3),
 toArray,
); // [1, 2]

// if you want to use asynchronous callback
await pipe(
 Promise.resolve([1, 2, 3, 4, 5, 6]),
 toAsync,
 takeWhile(async (a) => a < 3),
 toArray,
); // [1, 2]

// with toAsync
await pipe(
 [Promise.resolve(1), Promise.resolve(2), Promise.resolve(3),
Promise.resolve(4), Promise.resolve(5), Promise.resolve(6)],
 toAsync,
 takeWhile(a => a < 3),
 toArray,
); // [1, 2]

Try It

see pipe, toAsync, toArray