What Are the Key Differences Between Deferreds, Promises, and Futures in JavaScript?

Differences between Deferreds, Promises, and Futures in JavaScript

In JavaScript, promises handle asynchronous operations elegantly. However, there are subtler distinctions between Deferreds, Promises, and Futures that can be confusing.

Deferreds

The term "Deferred" is often used informally in implementations but rarely mentioned in standard definitions. A Deferred serves as an arbiter of promise resolution, allowing you to resolve or reject a promise. Some implementations make Deferreds also implement the Promise interface, while others keep them separate, requiring access to the Promise explicitly for then functionality.

Promises

Promises are the overarching concept encompassing the pattern of abstracting asynchronicity and error handling. A Promise represents the result of an asynchronous operation and exposes a then function to chain subsequent operations and handle its resolution or rejection.

Futures

"Future" is a lesser-used term that has sometimes been used interchangeably with "Promise," but it is gradually being replaced in favor of the more standardized term "Promise." However, some libraries, such as FutureJS, use "Future" as a generic term for abstracting synchronicity without providing then functionality, avoiding confusion with Promises' reliance on "thenables."

Conclusion

While the theory behind Deferreds, Promises, and Futures in JavaScript is conceptually similar, there are subtle differences in their implementation and terminology. Understanding these nuances can improve your comprehension and use of asynchronous programming techniques in JavaScript.

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