Then method
The JavaScript Promise then method registers fulfillment and rejection handlers and returns a new promise that represents their results.
Functional Programming in JavaScript
A Promise method that registers callbacks to run when the promise settles and returns a new promise for chaining.
- How it is used
- Structures dependent asynchronous work as linear transformations over values that arrive in the future.
- How deep it goes
- Explains callback arguments, serial chaining, and error placement, then extends the pattern to Promise.all.
- Examples
- Uses delayed resolution, promisified getJSON requests, chained student data processing, and concurrent grade retrieval.
- What you can do after
- Apply it via JavaScript Promise APIs to chain transformations, sequence requests, and handle failures.
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The Joy of JavaScript
A Promise method used to register fulfillment and rejection handlers and compose promise-based workflows.
- How it is used
- Uses Promise reactions to compose linear asynchronous transformations and centralize downstream error handling.
- How deep it goes
- Explains returned promises, value propagation, automatic flattening, broken chains, nested chains, and error recovery.
- Examples
- Demonstrates string transformations, fully linked and broken chains, nested promises, error propagation, and default-value recovery.
- What you can do after
- Apply it to build composable Promise pipelines, join nested asynchronous work, and diagnose detached handlers or unhandled rejections.
D3.js in Action, Third Edition
then() is a Promise method that registers callbacks for handling an asynchronous operation's fulfillment or rejection.
- How it is used
- Coordinates asynchronous D3 data loading with measurement, reorganization, and visualization construction.
- How deep it goes
- Explains Promise timing and callback access through a D3 workflow, stopping short of broader Promise behavior.
- Examples
- Uses a 33-row technology dataset, numeric count conversion, summary statistics, descending sorting, and a bar-chart handoff.
- What you can do after
- Apply it via JavaScript and D3 to manipulate a complete external dataset after loading finishes.
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Get Programming with JavaScript Next: New features of ECMAScript 2015, 2016, and beyond
A Promise method that registers callbacks to run when the promise is fulfilled or rejected, returning a new promise for chaining.
- How it is used
- Registers callbacks for eventual values from promise-based requests, allowing data loading and its use to happen at different times.
- How deep it goes
- Walks through fulfillment timing and an optional rejection callback; defers further error-handling techniques while identifying chaining in the advanced summary.
- Examples
- Uses an axios GitHub API request, an early-loading user view, a cached transaction, and a callback-to-promise JSON exercise.
- What you can do after
- Apply it via axios to consume responses, handle request errors, and use the same callback pattern for pending or resolved promises.
Secrets of the JavaScript Ninja, Second Edition
A Promise method that registers fulfillment and rejection handlers and returns a new promise for chaining.
- How it is used
- Registers fulfillment and rejection handlers and links dependent asynchronous steps into a promise chain.
- How deep it goes
- Explains handler behavior and returned-promise chaining through a multi-request example.
- Examples
- Uses a promise resolved with “Hattori” and chained JSON requests for ninja missions.
- What you can do after
- Apply promise chaining to sequence dependent JSON requests and route failures to catch.
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Related concepts
- microtask queueuses · A microtask queue is an event-loop queue that holds pending microtasks for processing after the current synchronous execution and before subsequent task processing.
- promiseproduces · A JavaScript Promise is an object representing the eventual completion or failure of an asynchronous operation and its resulting value or reason.
- callbackuses · A callback is a function or other callable supplied to software for invocation later in response to a specified event, condition, or point in execution.
- Promise#catchequivalent to · Promise#catch is a JavaScript Promise method that registers a handler for rejection and returns a Promise for the handler's outcome.
- async/awaitalternative to · 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.
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