@johngw/stream/dist/transformers/tapWhen.js

Reactive programming tools using the WHATWG Streams API.

import { WritableReadablePair } from './WritableReadablePair.js';
/**
 * Creates a {@see WritableReadablePair} that gives chunks to the `sink` when
 * when `predicate` passes. It will pass **all** chunks to the readable side.
 *
 * @remarks
 * A good way to signal that a sink is targeted to specific chunk types.
 *
 * @example
 * ```
 * myStream()
 *   .pipeThrough(tapWhen(isMyChunk, { write(myChunk) {} }))
 * ```
 */
export function tapWhen(predicate, sink) {
    return new WritableReadablePair({
        ...sink,
        async write(chunk, readableController, writableController) {
            if (predicate(chunk))
                await sink.write?.(chunk, writableController);
            readableController.enqueue(chunk);
        },
    });
}
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