What is map-limit?
The map-limit npm package allows you to map over an array of items with a limit on the number of concurrent asynchronous operations. This is useful for controlling the rate of operations, especially when dealing with APIs or other resources that have rate limits.
What are map-limit's main functionalities?
Basic Usage
This example demonstrates the basic usage of map-limit. It processes an array of numbers, doubling each one, but only allows two asynchronous operations to run concurrently.
const mapLimit = require('map-limit');
const tasks = [1, 2, 3, 4, 5];
const limit = 2;
function asyncTask(item, callback) {
setTimeout(() => {
callback(null, item * 2);
}, 1000);
}
mapLimit(tasks, limit, asyncTask, (err, results) => {
if (err) throw err;
console.log(results); // [2, 4, 6, 8, 10]
});
Error Handling
This example shows how to handle errors in map-limit. If an error occurs during the processing of an item, it is passed to the final callback.
const mapLimit = require('map-limit');
const tasks = [1, 2, 3, 4, 5];
const limit = 2;
function asyncTask(item, callback) {
setTimeout(() => {
if (item === 3) {
callback(new Error('An error occurred'));
} else {
callback(null, item * 2);
}
}, 1000);
}
mapLimit(tasks, limit, asyncTask, (err, results) => {
if (err) {
console.error(err.message); // 'An error occurred'
} else {
console.log(results);
}
});
Other packages similar to map-limit
async
The async package provides a wide range of asynchronous utilities, including the mapLimit function, which offers similar functionality to map-limit. It is more feature-rich and widely used, making it a good alternative if you need more than just map limiting.
p-limit
The p-limit package allows you to run multiple promise-returning & async functions with a concurrency limit. It is more modern and uses promises, making it a good choice for projects that prefer promise-based APIs over callback-based ones.
bluebird
Bluebird is a fully-featured promise library with a focus on performance and innovative features. It includes a map function with concurrency control, similar to map-limit, but also offers a wide range of other utilities for working with promises.