JavaScript 中的 Deferred、Promise 和 Future 有什么区别？

延期、承诺和期货之间有什么区别？
这三个背后是否有一个普遍认可的理论？

这些答案，包括选定的答案，有利于引入承诺 从概念上讲，但缺乏具体差异的具体内容 使用库实现它们时出现的术语（并且有are重要区别）。

既然还是不断发展的规范 http://dom.spec.whatwg.org/#open-issues，目前的答案来自于尝试调查这两个参考文献（例如维基百科 http://en.wikipedia.org/wiki/Futures_and_promises）和实现（如jQuery http://api.jquery.com/category/deferred-object/):

• Deferred: Never described in popular references, ^{1 http://en.wikipedia.org/wiki/Futures_and_promises 2 https://github.com/promises-aplus/promises-spec 3 http://dom.spec.whatwg.org/#promises 4 https://github.com/domenic/promises-unwrapping/blob/master/README.md} but commonly used by implementations as the arbiter of promise resolution (implementing resolve and reject). ^{5 http://dojotoolkit.org/reference-guide/1.9/dojo/Deferred.html 6 http://api.jquery.com/category/deferred-object/ 7 https://github.com/kriskowal/q}

  Sometimes deferreds are also promises (implementing then), ^{5 http://dojotoolkit.org/reference-guide/1.9/dojo/Deferred.html 6 http://api.jquery.com/category/deferred-object/} other times it's seen as more pure to have the Deferred only capable of resolution, and forcing the user to access the promise for using then. ^{7 https://github.com/kriskowal/q}

• Promise：对正在讨论的战略最包罗万象的词。

  A proxy object storing the result of a target function whose synchronicity we would like to abstract, plus exposing a then function accepting another target function and returning a new promise. ^{2 https://github.com/promises-aplus/promises-spec}

  示例来自CommonJS http://wiki.commonjs.org/wiki/Promises/A:

  > asyncComputeTheAnswerToEverything()
      .then(addTwo)
      .then(printResult);
  44
  

   

  Always described in popular references, although never specified as to whose responsibility resolution falls to. ^{1 http://en.wikipedia.org/wiki/Futures_and_promises 2 https://github.com/promises-aplus/promises-spec 3 http://dom.spec.whatwg.org/#promises 4 https://github.com/domenic/promises-unwrapping/blob/master/README.md}

  Always present in popular implementations, and never given resolution abilites. ^{5 http://dojotoolkit.org/reference-guide/1.9/dojo/Deferred.html 6 http://api.jquery.com/category/deferred-object/ 7 https://github.com/kriskowal/q}

• Future: a seemingly deprecated term found in some popular references ^{1 http://en.wikipedia.org/wiki/Futures_and_promises} and at least one popular implementation, ^{8 https://github.com/FuturesJS/FuturesJS} but seemingly being phased out of discussion in preference for the term 'promise' ^{3 http://dom.spec.whatwg.org/#promises} and not always mentioned in popular introductions to the topic.

  However, at least one library uses the term generically for abstracting synchronicity and error handling, while not providing then functionality. ^{10 https://github.com/angular/angular.js/blob/master/src/ngScenario/Future.js} It's unclear if avoiding the term 'promise' was intentional, but probably a good choice since promises are built around 'thenables.' ^{2 https://github.com/promises-aplus/promises-spec}

参考

1. 关于承诺和期货的维基百科 http://en.wikipedia.org/wiki/Futures_and_promises
2. 承诺/A+ 规格 http://promisesaplus.com/
3. Promise 的 DOM 标准 http://dom.spec.whatwg.org/#promises
4. DOM 标准 Promise 规范 WIP https://github.com/domenic/promises-unwrapping/blob/master/README.md
5. DOJO 工具包延期 http://dojotoolkit.org/reference-guide/1.9/dojo/Deferred.html
6. jQuery 延迟 http://api.jquery.com/category/deferred-object/
7. Q https://github.com/kriskowal/q
8. FutureJS https://github.com/FuturesJS/FuturesJS
10. AngularJS 集成测试的未来 https://github.com/angular/angular.js/blob/master/src/ngScenario/Future.js

其他可能令人困惑的事情

• Promise/A 和 Promise/A+ 之间的区别 http://promisesaplus.com/differences-from-promises-a

  （TL;DR，Promises/A+ 主要解决 Promises/A 中的歧义）