@kenavr/promise-operators v0.1.0

Operators for Promise chains

The project includes a couple of rxjs inspired operators for promises

Installation

npm i @kenavr/promise-operators

import { map } from '@kenavr/promise-operators';

Promise.resolve([1, 2, 3])
  .then(map(val => val + 1))
  .then(/*[2,3,4]*/);

Operators

Descriptions

All functions return a Promise making it simple to chain them.

map

Takes a mapping function and an array or object as value. If an array is passed it runs through the array and applies the mapping function to each value. If an object is passed the mapping function is applied once on the object.

Isolated Example

map(val => val + 1)(1).then(/* 2 */);

Example

Promise.resolve([1, 2, 3])
  .then(map(val => val + 1))
  .then(/*[2,3,4]*/);

filter

Takes a filter function and an array or object as value. If an array is passed its values are filtered based on the condition. If an object is passed the filter function is applied once on the object.

Isolated Example

filter(val => val < 10)([2, 3, 5, 7, 11, 13, 17, 19]).then(/* [2,3,5,7] */);

Example

Promise.resolve([2, 3, 5, 7, 11, 13, 17, 19])
  .then(filter(val => val < 10))
  .then(/*[2,3,5,7]*/);

reduce

Takes a reducer function with an initial value and an array or object as value. If an array is passed the function is applied on the array and return a single value. If an object is passed the reducer function is applied once on the object.

Isolated Example

reduce((sum, val) => sum + val, 0)([1, 2, 3, 4, 5]).then(/* 15 */);

Example

Promise.resolve([5, 4, 3, 2, 1])
  .then(reduce((product, val) => product * val, 1))
  .then(/* 120 */);

pipe

Takes a list of operators and executes them sequentially.

Isolated Example

pipe(
  map(val => val * 10),
  filter(val => val < 30)
)([1, 2, 3, 4, 5]).then(/* [10,20] */);

Example

Promise.resolve([1, 2, 3, 4, 5])
  .then(
    pipe(
      map(val => val * 10), // [10, 20, 30, 40, 50]
      filter(val => val < 30), // [10, 20]
      reduce((acc, val) => acc + val, 0) // 30
    )
  )
  .then(/* 30 */);

flatMap

Takes a mapping function that returns a Promise and an array or object as value. If an array is passed it runs through the array and applies the mapping function to each value. If an object is passed the mapping function is applied once on the object. The inner promises are resolved before returning a single Promise.

Isolated Example

flatMap(val => Promise.resolve(val + 1))(1).then(/* 2 */);

Example

Promise.resolve([1, 2, 3])
  .then(flatMap(val => Promise.resolve(val + 1)))
  .then(/*[2,3,4]*/);

parallel

Takes an array of functions and runs them parallel all receiving the same initial value

Isolated Example

const addOne = val => val + 1;
const subOneAsync = val => Promise.resolve(val - 1);

parallel([addOne, subOneAsync])(1).then(/* [2, 0]*/);

Example

const sum = array => array.reduce((sum, val) => sum + val, 0);
const multiply = array => array.reduce((sum, val) => sum * val, 1);

Promise.resolve([2, 3, 4])
  .then(parallel([sum, multiply]))
  .then(/*[ 9, 24 ]*/);

throwIf

Throws an error if the passed data doesn't meet the condition

Isolated Example

throwIf(val <= 5, 'Value is larger than 5')(10)
  .then(/**/)
  .catch(error => /* 'Value is larger than 5' */);

Example

Promise.resolve([2, 3, 4])
  .then(throwIf(array => array.length < 5, new Error('Array is too small!')))
  .then(/**/)
  .catch(error => /* 'Array is too small!' */);

tap

Executes a side effect without modifying the passed data

Isolated Example

tap(val => console.log('Value: ', val))(10) // Value: 10
  .then(/* 10 */);

Example

let counter = 0;

Promise.resolve([2, 3, 4])
  .then(tap(val => counter++))
  .then(/* [2, 3, 4] */);