Promise.map 没有返回正确的顺序

Question

使用蓝鸟我该如何做以下工作。

 groupCast = [Promise.resolve("name1"), Promise.resolve("name2"),Promise.resolve("name3")]

    Promise.map( groupCast , function (group){
        Promise.resolve($http.get("/getdata" , params:{group:group}))
               .then(function(response){ console.log(group," done")return response}))
        return response

        })
              .then(function(resp){console.log(resp)})

如果每个组对 http 调用的响应是 "one" 、 "two" 、 "three" 然后我们会期望：

"name1 done";
"name2 done";
"name3 done";
[ "one" , "two" ,"three" ]

但是我得到了

 [ "one" , "two" ,"three" ]
    "name1 done";
    "name2 done";
    "name3 done";

我该如何解决它。我不能使用异步等待，因为 IE 不支持它。

Answer 1

首先，您的代码格式让人很难看清发生了什么。让我稍微清理一下并添加一些 cmets，以便您查看发生了什么。

Promise.map(groupCast, function(group) {
  //the following kicks off a new promise, which is not chained to the current one
  Promise.resolve($http.get("/getdata", { params: { group: group } })).then(
    function(response) {
      console.log(group, " done");
      //you're returning response below, but it's not going anywhere!
      return response;
    }
  );
  //The current promise resolves right away, not waiting for the $http call.
  //Also, you're returning an undefined value here.
  return response;
}).then(function(resp) {
  //the prior promise resolves with undefined.
  console.log(resp);
});

现在让我们修复它，让 Promise 链正确。

Promise.map(groupCast, function(group) {
  // $http.get returns a promise already. No need to wrap it in one.
  // Also, let's go ahead and return the chained promise so the `map` function can wait for it.
  return $http.get("/getdata", { params: { group: group } })
    .then(function(response) {
        console.log(group, " done");
        return response;
      });
}).then(function(resp) {
  //the prior promise should now resolve as expected.
  console.log(resp);
});