when.js
A Promises/A+ and when() implementation with async utilities for JavaScript.
What is when.js?
When.js is a Promises/A+ compliant library that provides a fast `when()` implementation and additional async utilities for JavaScript. It simplifies managing complex callback flows by converting them into promise-based APIs, improving code readability and maintainability.
JavaScript developers working with asynchronous operations, especially those needing Promises/A+ compliance, ES6 Promise support, or utilities for handling promise collections and task execution.
Developers choose When.js for its combination of small size, high performance, debuggability, and rich features like promise collection resolution and callback transformation, making it a robust alternative to native promises or other promise libraries.
Overview
A solid, fast Promises/A+ and when() implementation, plus other async goodies.
Use Cases
Best For
- Converting Node-style callback APIs to promise-based APIs
- Handling arrays or hashes of promises with built-in resolution methods
- Executing asynchronous tasks in parallel or sequential order
- Adding ES6 Promise support to environments lacking native implementation
- Simplifying complex nested callback flows in JavaScript applications
- Debugging asynchronous code with enhanced debuggability features
Not Ideal For
- Projects exclusively using modern JavaScript with async/await and no need for promise chaining utilities
- Teams prioritizing minimal bundle size who can rely on native promises or lighter polyfills
- Applications requiring advanced promise features like cancellation or timeout management not supported by When.js
Pros & Cons
Pros
Ensures full interoperability with other promise libraries, making it a reliable choice for mixed environments as stated in the key features.
Provides a complete shim for environments lacking native ES6 Promise support, enhancing cross-platform compatibility without extra configuration.
Includes methods to resolve arrays, hashes, and sequences of promises, simplifying complex asynchronous operations as highlighted in the README examples.
Converts Node-style and callback-based APIs into promises, reducing callback hell and improving code maintainability with built-in utilities.
Emphasizes small size and high performance, offering efficient async utilities without unnecessary bloat per the project philosophy.
Cons
Lacks built-in support for promise cancellation or timeout management, which are available in competing libraries like Bluebird.
Has a smaller community and fewer third-party integrations compared to more popular promise libraries, potentially limiting resources and plugins.
Introduces an additional library in projects where native promises could suffice, increasing bundle size and maintenance complexity.
Frequently Asked Questions
Related Projects
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bluebird:bird: :zap: Bluebird is a full featured promise library with unmatched performance.
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rsvp.jsA lightweight library that provides tools for organizing asynchronous code
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