返回一个承诺抛出错误的 Promise [英] Return a Promise that promises to throw error

问题描述

我对使用 Promise 还很陌生，我主要坚持使用直接回调.下面的代码碰巧在 Angular Service 中找到，但这并不重要，主要是关于如何创建一个承诺会抛出某个错误的承诺.所以这就是合并回调时会发生的情况，从而避免了这个问题:

I am fairly new to using promises, I mostly stick to straight up callbacks. The following code happens to be found in an Angular Service, but that doesn't really matter that much, it's mostly regards how to create a promise that will promise to throw a certain error. So this is how it would happen with callbacks being incorporated, which avoids the problem:

var client = algolia.Client('ApplicationID', 'apiKey');


var indices = {

    users: client.initIndex('users'),
    topics: client.initIndex('topics')

}

return {

   search: function(indexName, searchTerms, cb){
       var index = indices[indexName];

       if(index){
          index.search(searchTerms).then(function handleSuccess(msg){
               cb(null,msg);
            }, function handleError(err){
               cb(err);
            }
       }
       else{
          cb(new Error('no matching index'));
       }

   }

...但是将上面的内容改为使用纯 Promises，我不知道该怎么做:

var client = algolia.Client('ApplicationID', 'apiKey');

var indices = {

    users: client.initIndex('users'),
    topics: client.initIndex('topics')

}

return {

   search: function(indexName, searchTerms){
       var index = indices[indexName];

       if(index){
          return index.search(searchTerms); //returns a promise
       }
       else{
          //if there is no matching index, how can I return a promise then will return an error?
       }

   }

我知道有不同的方法来构建代码来避免手头的问题，但我很好奇是否有直接解决它的方法.

I know there are different ways to structure the code to avoid the problem at hand but I am curious if there is way to solve it directly.

推荐答案

您可以注入 $q 服务并返回 $q.reject(reason)，例如:

You could inject $q service and return $q.reject(reason), e.g:

return $q.reject('NO_INDEX');

来自$q 文档:

创建一个因指定原因被拒绝的承诺.

Creates a promise that is resolved as rejected with the specified reason.

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