p-iteration 
Make array iteration easy when using async/await and promises
- Same functionality as the ES5 Array iteration methods we all know
- All the methods return a
Promise, making them awaitable and thenable - Allow the usage of async functions as callback
- Callbacks run concurrently
- Lightweight (no prd dependencies)
Install
$ npm install --save p-iteration
Usage
Smooth asynchronous iteration using async/await:
const { map } = require('p-iteration');
// map passing an async function as callback
function getUsers (userIds) {
return map(userIds, async userId => {
const response = await fetch(`/api/users/${userId}`);
return response.json();
});
}
// map passing a non-async function as callback
async function getRawResponses (userIds) {
const responses = await map(userIds, userId => fetch(`/api/users/${userId}`));
// ... do some stuff
return responses;
}
// ...const { filter } = require('p-iteration');
async function getFilteredUsers (userIds, name) {
const filteredUsers = await filter(userIds, async userId => {
const response = await fetch(`/api/users/${userId}`);
const user = await response.json();
return user.name === name;
});
// ... do some stuff
return filteredUsers;
}
// ...All methods return a Promise so they can just be used outside an async function just with plain Promises:
const { map } = require('p-iteration');
map([123, 125, 156], (userId) => fetch(`/api/users/${userId}`))
.then((result) => {
// ...
})
.catch((error) => {
// ...
});If there is a Promise in the array, it will be unwrapped before calling the callback:
const { forEach } = require('p-iteration');
const fetchJSON = require('nonexistent-module');
function logUsers () {
const users = [
fetchJSON('/api/users/125'), // returns a Promise
{ userId: 123, name: 'Jolyne', age: 19 },
{ userId: 156, name: 'Caesar', age: 20 }
];
return forEach(users, (user) => {
console.log(user);
});
}const { find } = require('p-iteration');
const fetchJSON = require('nonexistent-module');
function findUser (name) {
const users = [
fetchJSON('/api/users/125'), // returns a Promise
{ userId: 123, name: 'Jolyne', age: 19 },
{ userId: 156, name: 'Caesar', age: 20 }
];
return find(users, (user) => user.name === name);
}The callback will be invoked as soon as the Promise is unwrapped:
const { forEach } = require('p-iteration');
// function that returns a Promise resolved after 'ms' passed
const delay = (ms) => new Promise(resolve => setTimeout(() => resolve(ms), ms));
// 100, 200, 300 and 500 will be logged in this order
async function logNumbers () {
const numbers = [
delay(500),
delay(200),
delay(300),
100
];
await forEach(numbers, (number) => {
console.log(number);
});
}API
The methods are implementations of the ES5 Array iteration methods we all know with the same syntax, but all return a Promise. Also, with the exception of reduce(), all methods callbacks are run concurrently. There is a series version of each method, called: ${methodName}Series, series methods use the same API that their respective concurrent ones.
There is a link to the original reference of each method in the docs of this module:
Instance methods
Extending native objects is discouraged and I don't recommend it, but in case you know what you are doing, you can extend Array.prototype to use the above methods as instance methods. They have been renamed as async${MethodName}, so the original ones are not overwritten.
const { instanceMethods } = require('p-iteration');
Object.assign(Array.prototype, instanceMethods);
async function example () {
const foo = await [1, 2, 3].asyncMap((id) => fetch(`/api/example/${id}`));
}License
MIT Β© Antonio V