jQuery：deferred.always（）和deferred.then（）之间有什么区别？

Seems to me that both does the same thing.

在我看来，两者都做同样的事情。

Docs:

文档：

deferred.always()

deferred.always（）
deferred.then()

deferred.then（）

4 个解决方案

#1

It would seem that deferred.then() allows you to pass two separate callbacks for success and failure, whereas deferred.always() takes n number of callbacks which will all be called regardless of the outcome of the initial event.

似乎deferred.then（）允许您为成功和失败传递两个单独的回调，而deferred.always（）需要n个回调，无论初始事件的结果如何，都将调用它们。

I would say use deferred.always() in the cases where success/failure of the initial event are not important

我会说在初始事件的成功/失败并不重要的情况下使用deferred.always（）

#2

With .then() you can provide an individual callback for when the $.Deferred is resolved (done), and another for when the $.Deferred is rejected (fail).

使用.then（），您可以在$ .Deferred解析（完成）时提供单独的回调，并在$ .Deferred被拒绝（失败）时提供另一个回调。

.always(), on the other hand, allows you to provide a callback that always gets executed, whether the $.Deferred has been resolved or rejected. In other words, within this callback, it doesn't matter if the AJAX call has failed or has been been successfully executed.

另一方面，.always（）允许您提供始终执行的回调，无论$ .Deferred是否已被解决或拒绝。换句话说，在此回调中，AJAX调用失败或已成功执行无关紧要。

I tend to put code in .always() when I want that code to run everytime, and independently of whether the $.Deferred was resolved successfully or not. For example, to clear an AJAX loading indicator or to hide a progress bar. Using .then() you'd have something like this:

当我希望每次运行代码时，我倾向于将代码放在.always（）中，而不管$ .Deferred是否成功解析。例如，清除AJAX加载指示符或隐藏进度条。使用.then（）你会有这样的事情：

$.get("/some/url").then(function () { // done callback
  $(".progress-bar").hide();
}, function () { // fail callback
  $(".progress-bar").hide();
});

Whilst if you used .always(), you'd just need a single callback, because you always want to hide the progress bar, no matter if the $.Deferred was resolved or rejected:

虽然如果你使用.always（），你只需要一个回调，因为你总是想要隐藏进度条，无论$ .Deferred是否被解决或拒绝：

$.get("/some/url").always(function () {
  $(".progress-bar").hide();
});

#3

Prior to jQuery 1.8: .always(fn) is equivalent to .then(fn, fn)

在jQuery 1.8之前：.always（fn）相当于.then（fn，fn）

As of jQuery 1.8: .always(fn) is similar to .then(fn, fn) but it differs in what is returned (see http://api.jquery.com/deferred.then/ for details)

从jQuery 1.8开始：.always（fn）类似于.then（fn，fn），但返回的内容不同（详见http://api.jquery.com/deferred.then/）

#4

The big benefit of then (as of 1.8) is the capability to chain tasks explicitly because it returns a promise which will be resolved with the result of the callback(s)

当时（从1.8开始）的最大好处是能够明确地链接任务，因为它返回一个将通过回调的结果解决的promise。

Example from documentation:

文档示例：

var request = $.ajax( url, { dataType: "json" } ),
    chained = request.then(function( data ) {
      return $.ajax( url2, { data: { user: data.userId } } );
    });

chained.done(function( data ) {
  // data retrieved from url2 as provided by the first request
});

#1