sequential-promise-map

A simple sequential version of Promise.map, useful to transform an array of values into asynchronous promises, when you need to limit parallel execution of promise generators (eg to prevent hitting external resource thresholds, or to guarantee that things need to happen in a particular sequence).

The function has no dependencies so it will work in Node or browsers, as long as native Promises are supported.

Installation

npm install sequential-promise-map

Usage

sequentialPromiseMap(arrayOfValues, promiseGenerator, /*batchSize*/).then(....) 

• arrayOfValues should be an Array of elements that will be asynchronously processed
• promiseGenerator parameter should be a function to process each element of the array, receiving up to three arguments:

promiseGenerator = function(currentElement, indexOfCurrent, originalArray) {
  ...
}

• batchSize is an optional argument, a positive integer specifying the maximum batch size for parallel processing. If not set, the elements will be processed one by one. Set this to a value greater than 1 to allow for parallelisation.

The function will resolve will contain an array of Promise results, in the same order as the arguments, or reject with the first rejection.

Example

const sequentialPromiseMap = require('sequential-promise-map');
 
const fruits = ['apples', 'oranges', 'grapes'];
 
const invert = function (name/*, index, array*/) {
  return new Promise(resolve => {
    resolve(name.split('').reverse().join(''));
  });
};
 
sequentialPromiseMap(fruits, invert).then(results => console.log('got results', results));

License

MIT