async-functional

The asynchronous generator AsyncGenerator appears on many occasions. For example, fetching a set of records from a REST API, or dealing with database records. This package tries to give a functional flavor to dealing with such situations.

One can consider AysncGenerator as a stream. This library allows async generators to be treated in functional manner.

New JSON Path transformer added as functors so that it is possible to process set of JSONPaths together to create a single object.

Contents

Functional Operators

Inspired by rxjs and functional programming, this package gives operators such as map, filter, zip, take or takeWhile alongwith folds such as foldl. Hopefully, this allows programs to be implemented using simple for loop.

TODO - Controlled Parallalism

While working with multiple such async generators, this package will try to create a controlled parallalism.

Documentation

Prelude - A set of generic functions

Convert an Iterable into an async generator

  import {of} from 'async-functional';

  const input = of([1,2,3,4,5]);

  // Now you can iterate using for..await..of
  for await (const i of input)
    console.log("Output: " + i);

Collect the result of async generator into a promise

  import {of, collect} from 'async-functional';

  const input = of([1,2,3,4,5]);
  // Convert it back into a promise
  const result = await collect(input);

Functors and folds - Higher order functions

Functors and other higher order functions to process async generator.

Create a functor - Lift a function to process async generator

  import {functor, of} from 'async-functional';

  // Create a async generator from an array
  const input = of([1, 2, 3, 4, 5]);
  // A simple function to square the numbers
  const square = (x: number) => x * x;
  // Use functor to lift square to squareMap
  const squareMap = functor(square);

  // Use map to square each element
  for await (const i of squareMap(input)) {
    console.log('output = ' + i);
  }

Use map as a functor

import {map, of} from 'async-functional';

// Create a async generator from an array
const input = of([1, 2, 3, 4, 5]);

// Use map to square each element
for await (const i of map(x => x * x, input)) {
  console.log('output = ' + i);
}

Use filter to selectively iterate over elements

import {filter, of} from 'async-functional';

// Create a async generator from an array
const input = of([1, 2, 3, 4, 5]);

// Filter to remove odd elements
const evenFilter = (x: number) => x % 2 == 0

// Use map to square each element
for await (const i of filter(evenFilter, input)) {
  console.log('output = ' + i);
}

// Output =>
// output = 2
// output = 4

JSON Path transformation

import {jsonPathNumber, jsonTransform, jsonPathBoolean} from '..';

  const numberMap = jsonPathNumber('$.number', 'mynumber');
  const booleanMap = jsonPathBoolean('$.result', 'myboolean');
  const transf = jsonTransform(nkeyMap, bkeyMap);
  const input = {
    number: 101.0,
    result: false,
  };
  const output = transf(input);

  // Should see { mynumber: 101.0, myboolean: false }