angularJS中$ q.when和$ q.defer之间的差异

I am seeing angularJS files where in some places reviewer has commented these 3 lines:

我看到angularJS文件，在某些地方，评论者评论了这3行：

var deferred = $q.defer();
deferred.resolve(BrandList);
return deferred.promise;

and replaced with this one:

并替换为这一个：

return $q.when(BrandList);

I would like to understand the difference between two. Do both serve same purpose? Which should be used when?

我想了解两者之间的区别。两者都有同样的目的吗？哪个应该用？

2 个解决方案

#1

Ben Nadal does a great job of explaining this here.

本纳达尔在这里做了很好的解释。

In his words:

用他的话说：

The $q.when() method doesn't just create a promise that is immediately resolved; rather, it normalizes a value that may or may not be a "thenable" object. If the given value is a promise, $q.when() will properly chain off of it. If the given value is not a promise, $q.when() will create promise resolved with the given value.

$ q.when（）方法不只是创建一个立即解决的promise;相反，它将一个值标准化，该值可能是也可能不是“可以”的对象。如果给定的值是一个promise，$ q.when（）将正确地链接它。如果给定的值不是promise，$ q.when（）将创建使用给定值解析的promise。

So essentially it takes either promises or non-promises and does some magic to make sure they are either resolved or promise wrapped so as not to break the promise chain.

所以基本上它需要承诺或非承诺，并做一些魔术，以确保它们被解决或承诺包装，以便不打破承诺链。

#2

$q.defer() is appropriate when you want to decorate a function to use promises instead of callbacks. Usually, you will specify a deferred.resolve() and a deferred.reject(), and maybe even a deferred.notify().

当你想装饰一个函数来使用promises而不是回调时，$ q.defer（）是合适的。通常，您将指定deferred.resolve（）和deferred.reject（），甚至可能是deferred.notify（）。

$q.when() is appropriate when you want to immediately create a new promise and resolve it to a value. EDIT it also normalizes variables into promises, which is useful if the variable may or may not be a promise. See Jim's answer.

当您想立即创建新承诺并将其解析为值时，$ q.when（）是合适的。编辑它还可以将变量规范化为承诺，如果变量可能是也可能不是承诺，这很有用。看到吉姆的回答。

$q.when() seems to be appropriate for your case.

$ q.when（）似乎适合你的情况。

#1