抓后，然后执行 [英] Executing then after catch

问题描述

我有以下的小提琴：
http://jsfiddle.net/thelgevold/3uv9nnjm/6/

angular.module('hello',[]).controller('helloController',function($q){

    console.clear();
    function someService(){
       var deferred = $q.defer();
       deferred.reject({e:'error'}); 
       return deferred.promise;
    } 

    function callService(){
        return someService().then(function(obj){
           console.log('first then');
        }).
        catch(function(e){
            console.log('error1');
            var deferred = $q.defer();
            deferred.reject({e:'error'}); 
            return deferred.promise;
        });
    }

    callService().catch(function(e){
      console.log('error2');
    }).then(function(e){
      console.log('second then');
    });

});

它本质上只是一个快速$ Q承诺POC。我的问题是：为什么最后再子句时得到的承诺被拒绝叫什么名字？输出如下所示：

It's essentially just a quick $q promise POC. My question is: Why does the last then clause get called when the promise is rejected? The output is as follows:

ERROR1

误差2

第二次再

我明白为什么ERROR1 /误差2打印，但我认为第二个字符串，然后不应该因为打印的承诺遭到了拒绝。我认为这将省去第二次则，为第一则省略同样的道理。
有什么想法？

I understand why error1/error2 are printed, but I thought the second then string should not be printed since the promise was rejected. I thought it would omit "second then" for the same reason the "first then" is omitted. Any thoughts?

推荐答案

在我开始之前，不这样做：

Before I get started, don't do this:

var deferred = $q.defer();
deferred.reject({e:'error'}); 
return deferred.promise;

做到这一点：

return $q.reject({e:'error'});

或者preferably，这样的：

Or preferably, this:

return $q.reject(new Error('error'));

<一个href=\"http://stackoverflow.com/questions/23803743/what-is-the-deferred-antipattern-and-how-do-i-avoid-it\">Beware递延反模式。

现在，在回答你的问题。

---

在 .catch（）您的来电 callService（）正在迎头赶上错误，而不是产生一个新的错误后。它基本上是处理的错误，下面。然后（）的处理程序是免费的调用。

Now, for the answer to your question.

---

The .catch() after your call to callService() is catching the error and not producing a new error. It has essentially "handled" the error, and the following .then() handler is free to be called.

同步code相当于你的例子是：

The synchronous code equivalent of your example would be:

function someService() {
    throw {e: 'error'};
}

function callService(){
    try {
        var obj = someService();
        console.log('first then');
    } catch (e) {
        console.log('error1');
        throw {e: 'error'};
    }
}

var e;
try {
    e = callService();
} catch (e) {
    console.log('error2');
}

console.log('second then');

我认为，如果你看它这样，它非常有意义。

I think that if you look at it this way, it makes perfect sense.

在承诺/ A +规格中的有关内容这里。对于所有意图和目的，可以查看抓处理程序，同样的事情作为一个 onRejected 处理程序：

The relevant text in the Promises/A+ spec is here. For all intents and purposes, you can view the catch handler as the same thing as an onRejected handler:

2.2.7。那么必须返回一个承诺[3.3]。

2.2.7. then must return a promise [3.3].

promise2 = promise1.then（onFulfilled，onRejected）;

2.2.7.1。如果任onFulfilled或onRejected返回一个值x，运行无极解决程序[解析]（promise2，X）。

2.2.7.1. If either onFulfilled or onRejected returns a value x, run the Promise Resolution Procedure [[Resolve]](promise2, x).

基本上，你的 onRejected 处理程序返回值未定义，因此所产生的诺言赶上（）与价值解析未定义。

Basically, your onRejected handler is "returning" the value undefined, so the promise produced by catch() resolves with the value undefined.

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