I intend to use this space to document my promise modules, useful promise patterns, and how to solve common problems. For now though, you can see all my promise modules below.

• Packages
• FAQ

Not accepting additions, but happy to take requests.

• pify: Promisify a callback-style function
• delay: Delay a promise a specified amount of time
• yoctodelay: Delay a promise a specified amount of time
• p-map: Map over promises concurrently
• p-all: Run promise-returning & async functions concurrently with optional limited concurrency
• p-event: Promisify an event by waiting for it to be emitted
• p-debounce: Debounce promise-returning & async functions
• p-throttle: Throttle promise-returning & async functions
• p-timeout: Timeout a promise after a specified amount of time
• p-retry: Retry a promise-returning or async function
• p-any: Wait for any promise to be fulfilled
• p-some: Wait for a specified number of promises to be fulfilled
• p-mutex: Ensure that only one operation accesses a particular resource at a time
• p-locate: Get the first fulfilled promise that satisfies the provided testing function
• p-limit: Run multiple promise-returning & async functions with limited concurrency
• p-series: Run promise-returning & async functions in series
• p-memoize: Memoize promise-returning & async functions
• p-pipe: Compose promise-returning & async functions into a reusable pipeline
• p-props: Like Promise.all() but for Map and Object
• p-waterfall: Run promise-returning & async functions in series, each passing its result to the next
• p-cancelable: Create a promise that can be canceled
• p-progress: Create a promise that reports progress
• p-reflect: Make a promise always fulfill with its actual fulfillment value or rejection reason
• p-filter: Filter promises concurrently
• p-reduce: Reduce a list of values using promises into a promise for a value
• p-settle: Settle promises concurrently and get their fulfillment value or rejection reason with optional limited concurrency
• p-map-series: Map over promises serially
• p-each-series: Iterate over promises serially
• p-times: Run promise-returning & async functions a specific number of times concurrently
• p-lazy: Create a lazy promise that defers execution until .then() or .catch() is called
• p-whilst: While a condition returns true, calls a function repeatedly, and then resolves the promise
• p-do-whilst: Calls a function repeatedly while a condition returns true and then resolves the promise
• p-forever: Run promise-returning & async functions repeatedly until you end it
• p-wait-for: Wait for a condition to be true
• p-min-delay: Delay a promise a minimum amount of time
• p-try: Promise.try() ponyfill - Starts a promise chain
• p-race: A better Promise.race()
• p-immediate: Returns a promise resolved in the next event loop - think setImmediate()
• p-time: Measure the time a promise takes to resolve
• p-defer: Create a deferred promise
• p-is-promise: Check if something is a promise
• p-state: Inspect the state of a promise
• p-queue: Promise queue with concurrency control
• make-synchronous: Make an asynchronous function synchronous

You should generally avoid using .then except in edge cases.

• p-catch-if: Conditional promise catch handler
• p-if: Conditional promise chains
• p-tap: Tap into a promise chain without affecting its value or state
• p-log: Log the value/error of a promise
• p-break: Break out of a promise chain

This is a good use-case for p-map. You might ask why you can't just specify an array of promises. Promises represent values of a computation and not the computation itself - they are eager. So by the time p-map starts reading the array, all the actions creating those promises have already started running. p-map works by executing a promise-returning function in a mapper function. This way the promises are created lazily and can be concurrency limited. Check out p-all instead if you're using different functions to get each promise.

import pMap from 'p-map';

const urls = [
	'https://sindresorhus.com',
	'https://avajs.dev',
	'https://github.com',
	…
];

console.log(urls.length);
//=> 100

const mapper = url => fetchStats(url); //=> Promise

const result = await pMap(urls, mapper, {concurrency: 5});

console.log(result);
//=> [{url: 'https://sindresorhus.com', stats: {…}}, …]