Promises

Awesome Promises

A curated list of useful resources for JavaScript Promises

Inspired by the awesome list thing. Not to be confused with other awesome promises like "I promise you a million dollars" or "I promise you'll stay fit and never have to go to the gym again".

Resources, Blogs, and Books

For beginners

• Promise Cookbook - The why, what, and how. "A brief introduction [...] primarily aimed at frontend developers".
• Promises for Asynchronous Programming - Chapter from Exploring ES6
• You Don't Know JS: Promises - Chapter from You Don't Know JS: Async & Performance
• JavaScript Promises: an Introduction - Basics of JavaScript's native promise implementation.
• JavaScript with Promises - from O'Reilly. Short and to-the-point. Uses native and bluebird.
• Promise it won't hurt - An interactive nodeschool workshop
• ES6 Kata Promises - Promises Katas : Basics
• ES6 Promises in Depth
• An Incremental Tutorial on Promises - An FAQ styled tutorial for beginners.

Deep Dive

• Promise Fun - @sindresorhus's notes, patterns, and solutions to common Promise problems
• You're Missing the Point of Promises - Promises are much more than callback aggregation, and that jQuery's implementation (prior to 3.0) isn't enough.
• We have a problem with promises - "Many of us are using promises without really understanding them."
• Promise anti-patterns - Common misuses and how to avoid them.
• Promise anti-patterns (2) - Another set of promises anti-patterns
• Promise Ponderings, (Anti-)Patterns, and Apologies - Promise behaviour demonstrated and explained by common questions and their answers.
• Javascript Promises...In Wicked Detail - Recreate the promise implementation
• Writing Promise-Using Specifications - "This document gives guidance on how to write specifications that create, accept, or manipulate promises"
• Async functions - making promises friendly

References

• Promises/A+ specification
• caniuse promises
• Fates and States - Quick definitions of possible states.
• Promisees - Promise visualization playground for the adventurous.

Promises/A+ Implementations (ES6/ES2015 compatible)

Strict Implementations

These implement no more or less than the es6 spec. They make great polyfills and are exceptionally compatible with native promises.

• pinkie - Ponyfill. Node-oriented, but browserifyable. Extremely small implementation.
• native-promise-only - Polyfill. Browser and node-compatible.
• es6-promise - Opt-in polyfill. A strict-spec subset of rsvp.js.
• lie - Small, browserifyable with an opt-in polyfill.

Implementations with extras

All of these provide more features than the language yet remain compatible. Node + Browsers for all.

• bluebird - Fully featured, extremely performant. Long stack traces & generator/coroutine support.
• creed - Hyper performant & full featured like Bluebird, but FP-oriented. Coroutines, generators, promises, ES2015 iterables, & fantasy-land spec.
• rsvp.js - Lightweight with a few extras. Compatible down to IE6!
• Q - One of the original implementations. Long stack traces and other goodies.
• then/promise - Small with nodeify, denodify and done() additions.
• when.js - Packed with control flow, functional, and utility methods.

Fallbacks

• native-or-bluebird - Helps transition to completely native.
• pinkie-promise - Use native, or fall back to pinkie. Great for node library authors.
• any-promise - Loads the first available implementation. Safe for browserify.

Convenience Utilities

Native and strictly spec-compliant promises are awesome for compatibility, future-proofness, library authors, and browsers. However, libraries like bluebird patch goodies onto the Promise constructor and prototype. Solution? tiny modules of course!

sindresorhus's many Promise utilities (see notes)

• delay - Delay a promise a specified amount of time.
• pify - Promisify ("denodify") a callback-style function.
• loud-rejection - Make unhandled promise rejections fail loudly instead of the default silent fail.
• hard-rejection - Make unhandled promise rejections fail hard right away instead of the default silent fail
• p-queue - Promise queue with concurrency control
• p-break - Break out of a promise chain
• p-lazy - Create a lazy promise that defers execution until .then() or .catch() is called
• p-defer - Create a deferred promise
• p-if - Conditional promise chains
• p-tap - Tap into a promise chain without affecting its value or state
• p-map - Map over promises concurrently
• p-all - Run promise-returning & async functions concurrently with optional limited concurrency
• p-limit - Run multiple promise-returning & async functions with limited concurrency
• p-times - Run promise-returning & async functions a specific number of times concurrently
• p-catch-if - Conditional promise catch handler
• p-time - Measure the time a promise takes to resolve
• p-log - Log the value/error of a promise
• p-filter - Filter promises concurrently
• p-settle - Settle promises concurrently and get their fulfillment value or rejection reason
• p-memoize - Memoize promise-returning & async functions
• p-whilst - Calls a function repeatedly while a condition returns true and then resolves the promise
• p-throttle - Throttle promise-returning & async functions
• p-debounce - Debounce promise-returning & async functions
• p-retry - Retry a promise-returning or async function
• p-wait-for - Wait for a condition to be true
• p-timeout - Timeout a promise after a specified amount of time
• p-race - A better Promise.race()
• p-try - Promise#try() ponyfill - Starts a promise chain
• p-finally - Promise#finally() ponyfill - Invoked when the promise is settled regardless of outcome
• p-any - Wait for any promise to be fulfilled
• p-some - Wait for a specified number of promises to be fulfilled
• p-pipe - Compose promise-returning & async functions into a reusable pipeline
• p-each-series - Iterate over promises serially
• p-map-series - Map over promises serially
• p-reduce - Reduce a list of values using promises into a promise for a value
• p-props - Like Promise.all() but for Map and Object

Others

• promise-method - Standalone bluebird.method. Turn a synchronously-returning method into a promise-returning one.
• is-promise - Determine if something looks like a Promise.
• sprom - Resolve when a stream ends. Optional buffering (be careful with this!)
• task.js - Write async functions in a blocking style using promises and generators. Like bluebird.coroutine.
• co - Like task.js and bluebird.coroutine, but supports thunks too.
• lie-fs - Promise wrappers for Node's FS API.
• promise-do-until - Calls a function repeatedly until a condition returns true and then resolves the promise.
• promise-do-whilst - Calls a function repeatedly while a condition returns true and then resolves the promise.
• promise-semaphore - Push a set of work to be done in a configurable serial fashion
• promise-nodeify - Standalone nodeify method which calls a Node-style callback on resolution or rejection.

License

Licensed under the Creative Commons CC0 License.