p-each-series

What is p-each-series?

The p-each-series package is a utility that allows you to iterate over a list of items and apply an asynchronous function to each item in series, meaning one after the other. It returns a Promise that resolves when all the iterations are completed. This is particularly useful when you need to perform async operations in a specific order.

What are p-each-series's main functionalities?

Iterating over an array in series

This code sample demonstrates how to use p-each-series to iterate over an array of items and log each item to the console one by one. After all items have been logged, it prints 'Done:' followed by the original array.

const pEachSeries = require('p-each-series');

const logItem = async item => {
  console.log(item);
  return item;
};

(async () => {
  const result = await pEachSeries(['a', 'b', 'c'], logItem);
  console.log('Done:', result);
})();

Handling asynchronous operations in series

This code sample shows how p-each-series can be used to perform asynchronous operations on each item in an array, with each operation being delayed by 1 second. It logs a message after each item is processed and finally logs that all items have been processed.

const pEachSeries = require('p-each-series');

const asyncOperation = item => new Promise(resolve => {
  setTimeout(() => {
    console.log(`Processed ${item}`);
    resolve(item);
  }, 1000);
});

(async () => {
  const result = await pEachSeries(['item1', 'item2', 'item3'], asyncOperation);
  console.log('All items have been processed:', result);
})();

Other packages similar to p-each-series

async

The 'async' package provides a wide range of functions for working with asynchronous code. Its 'eachSeries' function is similar to p-each-series, but 'async' offers many other patterns for control flow as well, making it more versatile but also larger in size.

bluebird

Bluebird is a fully-featured promise library that includes utilities for serial and parallel flow control. Its 'mapSeries' function can be used similarly to p-each-series for serial iteration, but Bluebird also provides a plethora of other features for promise manipulation and optimization.

p-series

p-series is another package that runs promise-returning & async functions in series. It is similar to p-each-series but is designed to run an array of functions rather than mapping over an array of values.

README

p-each-series

Iterate over promises serially

Useful as a side-effect iterator. Prefer p-map if you don't need side-effects, as it's concurrent.

Install

$ npm install p-each-series

Usage

import pEachSeries from 'p-each-series';

const keywords = [
	getTopKeyword(), //=> Promise
	'rainbow',
	'pony'
];

const iterator = async element => saveToDiskPromise(element);

console.log(await pEachSeries(keywords, iterator));
//=> ['unicorn', 'rainbow', 'pony']

API

pEachSeries(input, iterator)

Returns a Promise that is fulfilled when all promises in input and ones returned from iterator are fulfilled, or rejects if any of the promises reject. The fulfillment value is the original input.

input

Type: Iterable<Promise | unknown>

Iterated over serially in the iterator function.

iterator(element, index)

Type: Function

Return value is ignored unless it's Promise, then it's awaited before continuing with the next iteration.

pEachSeries.stop

Stop iterating through items by returning pEachSeries.stop from the iterator function.

import pEachSeries from 'p-each-series';

// Logs `a` and `b`.
const result = await pEachSeries(['a', 'b', 'c'], value => {
	console.log(value);

	if (value === 'b') {
		return pEachSeries.stop;
	}
});

console.log(result);
//=> ['a', 'b', 'c']

Related

• p-map-series - Map over promises serially
• p-series - Run promise-returning & async functions in series
• p-pipe - Compose promise-returning & async functions into a reusable pipeline
• p-waterfall - Run promise-returning & async functions in series, each passing its result to the next
• p-reduce - Reduce a list of values using promises into a promise for a value
• p-map - Map over promises concurrently
• More…