Promise
A JavaScript Promise is an object representing the eventual completion or failure of an asynchronous operation and its resulting value or reason.
The Joy of JavaScript
- How it is used
- Models single asynchronous results as composable chains instead of nested callbacks.
- How deep it goes
- Works through construction, settlement, chaining, and nested-Promise flattening, while leaving detailed event-loop scheduling aside.
- Examples
- Uses Promise construction, chained string transformations, and a filesystem workflow that checks access, reads, counts, and catches errors.
- What you can do after
- Apply it via the JavaScript Promise API to compose asynchronous operations and handle their failures in a flat chain.
Secrets of the JavaScript Ninja, Second Edition
A JavaScript object representing the eventual completion or failure of an asynchronous operation and its resulting value.
- How it is used
- Organizes asynchronous browser work so dependent server requests need not block the UI or rely on nested callbacks.
- How deep it goes
- Works through construction, state transitions, rejection, and a promise-returning JSON request, then extends to chains and generator coordination.
- Examples
- Uses a delayed timer, explicit and exception-driven rejection, and an XMLHttpRequest-based JSON fetch.
- What you can do after
- Build it from scratch: wrap an XMLHttpRequest in a promise and handle successful responses, request failures, and invalid JSON.
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Get Programming with JavaScript Next: New features of ECMAScript 2015, 2016, and beyond
- How it is used
- Uses promises to pass around eventual asynchronous results and handle them when needed.
- How deep it goes
- Works through consumption, errors, helpers, chains, and constructor-based wrappers; stops short of detailed event-loop internals.
- Examples
- Demonstrates GitHub organization requests, cached transactions, image loading, and a canvas fade.
- What you can do after
- Build it from scratch with new Promise, or apply it via axios and Promise helpers to coordinate asynchronous work.
Functional Programming in JavaScript
- How it is used
- Coordinates asynchronous operations while supporting composition, chaining, and centralized failure handling.
- How deep it goes
- Explains lifecycle, callbacks, chaining, concurrency, and practical wrappers, but stops short of detailed implementation internals.
- Examples
- Uses delayed callbacks, XMLHttpRequest, student records, browser storage, chained requests, and Promise.all().
- What you can do after
- Builds and composes asynchronous JavaScript operations with then, catch, and Promise.all().
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D3.js in Action, Third Edition
A JavaScript Promise is an object representing the eventual completion or failure of an asynchronous operation and its resulting value.
- How it is used
- Coordinates asynchronous D3 data loading with later measurement, reorganization, and visualization.
- How deep it goes
- Defines the returned object and demonstrates then() callbacks, but does not develop rejection handling or Promise internals.
- Examples
- Uses d3.csv(), row conversion, d3.autoType, console logging, sorting, and createViz() with technology and temperature datasets.
- What you can do after
- Apply it via D3 to wait for loaded data before measuring, sorting, transforming, or drawing a visualization.
API Design Patterns
A promise is an object or abstraction representing the eventual completion or failure of an asynchronous computation.
- How it is used
- Uses promises to represent asynchronous work without immediately blocking program execution.
- How deep it goes
- Explains resolution, rejection, awaiting, callbacks, polling, and waiting, but does not descend into promise implementation internals.
- Examples
- Demonstrates factorization, await, then/catch callbacks, and a chat-room operation tracked through an API.
- What you can do after
- Apply promises through await or callbacks, and evaluate API operations through polling or a wait method.
Rust Servers, Services, and Apps
A JavaScript promise is an object representing the eventual completion or rejection of an asynchronous operation and its resulting value.
- How it is used
- Uses promises to explain nonblocking browser requests and to compare JavaScript asynchronous processing with Rust async code.
- How deep it goes
- Defines promise semantics and contrasts them with futures, but stops short of JavaScript promise construction or chaining APIs.
- Examples
- Uses browser URL fetches and image loading as concrete asynchronous operations represented by promises.
- What you can do after
- Evaluate how JavaScript promises correspond to Rust futures while recognizing rejection as a higher-level promise behavior.
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Related concepts
- Promise.allused by · Promise.all is a JavaScript static method that returns a promise fulfilled with an array of results when all input promises fulfill, or rejected if any input promise rejects.
- Promise.raceused by · Promise.race is a JavaScript static method that returns a promise settled with the outcome of the first input promise or thenable to settle.
- async/awaitproduced by · Async/await is language syntax for expressing asynchronous computations that suspend at awaited operations and resume when they can proceed without blocking the execution thread.
- dynamic importproduced by · Dynamic import is a language feature that asynchronously loads a module at runtime and returns a promise for its module namespace.
- async iteratorused by · An async iterator is an iterator interface that asynchronously produces successive values for consumption over time.
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