@naturalcycles/nodejs-lib/dist/stream/transform/transformTap.js

Standard library for Node.js

import { Transform } from 'node:stream';
/**
 * Similar to RxJS `tap` - allows to run a function for each stream item, without affecting the result.
 * Item is passed through to the output.
 *
 * Can also act as a counter, since `index` is passed to `fn`
 */
export function transformTap(fn, opt = {}) {
    const { logger = console, highWaterMark = 1 } = opt;
    let index = -1;
    return new Transform({
        objectMode: true,
        highWaterMark,
        async transform(chunk, _, cb) {
            try {
                await fn(chunk, ++index);
            }
            catch (err) {
                logger.error(err);
                // suppressed error
            }
            cb(null, chunk);
        },
    });
}
/**
 * Sync version of transformTap
 */
export function transformTapSync(fn, opt = {}) {
    const { logger = console, highWaterMark = 1 } = opt;
    let index = -1;
    return new Transform({
        objectMode: true,
        highWaterMark,
        transform(chunk, _, cb) {
            try {
                fn(chunk, ++index);
            }
            catch (err) {
                logger.error(err);
                // suppressed error
            }
            cb(null, chunk);
        },
    });
}