Stream API

Type-safe API for processing Iterable data (Arrays, Sets, Maps, Iterables) similarly to Java 8 Stream API, LINQ or Kotlin Sequences.

• API Docs
• Benchmarks

Classic Javascript solution

const result = [1, 2, 3].filter(x => x % 2 === 0).map(x => x * 2);

Stream API solution

Creating a Stream object

import {Stream, of, from} from '@szilanor/stream';

let stream: Stream<number>;
stream = new Stream([1, 2, 3]); // With constructor;
stream = of(1, 2, 3); // With the 'of' creator function
stream = from([1, 2, 3]); // With the 'from' creator function

Operations on stream entries for the same result

import {filter, map, compound} from '@szilanor/stream';

stream = stream.pipe(
  filter(x => x % 2 === 0),
  map(x => x * 2)
);

Process the stream for the same result

import {toArray} from '@szilanor/stream';

// With a collector
result = stream.collect(toArray());

// Using for..of
let result = [];
for (let entry of stream) {
  result.push(entry);
}

// Using spread operator
result = [...stream];

Why Stream API?

• Can achieve faster results due to sequential processing

let allEven: boolean;
const input = [1, 2, 3, 4, 5];

// Classic JS maps all the entries first then returns false
allEven = input.map(x => x + 1).every(x => x % 2 === 0);

// vs Stream API maps only the first element then returns false
allEven = from(input)
  .pipe(map(x => x + 1))
  .collect(all(x => x % 2 === 0));

• More readable code

import {from, distinct, collect} from '@szilanor/stream';

// Filtering duplicates and group them by whether they are even or odd
const input = [1, 1, 1, 1, 2, 3, 4, 4, 5];

// Classic JS
const resultClassic: Map<string, number[]> = new Map<string, number[]>();
Array.from(new Set<number>(input)).forEach(x => {
  const key = x % 2 === 0 ? 'even' : 'odd';
  resultClassic.set(key, [...(resultClassic.get(key) || []), x]);
});

// Stream API
const resultStreamApi: Map<string, number[]> = from(input)
  .pipe(distinct())
  .collect(groupBy(x => (x % 2 === 0 ? 'even' : 'odd')));

• You can create your own operators and collectors if you don't find what you need

import {CollectorFunction, OperationFunction} from '@szilanor/stream';

const myAwesomeCollector: CollectorFunction<unknown, unknown> = {
  /* your own implementation */
};
const myAwesomeOperation: OperationFunction<unknown, unknown> = {
  /* your own implementation */
};

const result = of(1, 2, 3)
  .pipe(myAwesomeOperation())
  .collect(myAwesomeCollector());