@naturalcycles/nodejs-lib/dist/stream/transform/transformMap.d.ts

Standard library for Node.js

import { ErrorMode, Mapper, Predicate } from '@naturalcycles/js-lib';
import { TransformTyped } from '../stream.model';
export interface TransformMapOptions<OUT = any> {
    /**
     * @default true
     */
    objectMode?: boolean;
    /**
     * @default false
     * Set true to support "multiMap" - possibility to return [] and emit 1 result for each item in the array.
     */
    flattenArrayOutput?: boolean;
    /**
     * Predicate to filter outgoing results (after mapper).
     * Allows to not emit all results.
     *
     * @default to filter out undefined/null values, but pass anything else
     *
     * Set to `r => r` (passthrough predicate) to pass ANY value (including undefined/null)
     */
    predicate?: Predicate<OUT>;
    /**
     * Number of concurrently pending promises returned by `mapper`.
     *
     * @default 16 (to match default highWatermark option for objectMode streams)
     */
    concurrency?: number;
    /**
     * @default THROW_IMMEDIATELY
     */
    errorMode?: ErrorMode;
    /**
     * If defined - will be called on every error happening in the stream.
     * Called BEFORE observable will emit error (unless skipErrors is set to true).
     */
    onError?: (err: Error) => any;
    /**
     * Progress metric
     * @default `stream`
     */
    metric?: string;
    /**
     * If defined - called BEFORE `final()` callback is called.
     */
    beforeFinal?: () => any;
    /**
     * If defined - called AFTER final chunk was processed.
     */
    afterFinal?: () => any;
}
/**
 * Like pMap, but for streams.
 * Inspired by `through2`.
 * Main feature is concurrency control (implemented via `through2-concurrent`) and convenient options.
 * Using this allows native stream .pipe() to work and use backpressure.
 *
 * Only works in objectMode (due to through2Concurrent).
 *
 * Concurrency defaults to 16.
 *
 * If an Array is returned by `mapper` - it will be flattened and multiple results will be emitted from it. Tested by Array.isArray().
 */
export declare function transformMap<IN = any, OUT = IN>(mapper: Mapper<IN, OUT>, opt?: TransformMapOptions<OUT>): TransformTyped<IN, OUT>;