angular.js中promise多个then的问题

Question

<div ng-app="MyApp">
  <div ng-controller="MyController">
    <label for="flag">成功
      <input id="flag" type="checkbox" ng-model="flag" /><br/>
    </label>
    <div ng-cloak>
      {{status}}
    </div>
    <hr/>
    <button ng-click="handle()">点击我</button>
  </div>
</div>
<script>
  angular.module("MyApp", [])
    .controller("MyController", ["$scope", "$q", function ($scope, $q) {
      $scope.flag = true;
      $scope.handle = function () {
        var deferred = $q.defer();
        var promise = deferred.promise;

        if ($scope.flag) {
          deferred.resolve("you are lucky!");
        } else {
          deferred.reject("sorry, it lost!");
        }
        promise.then(function (result) {
          result = result + "you have passed the first then()";
          $scope.status = result;
          return result;
        }, function (error) {
          error = error + "failed but you have passed the first then()";
          $scope.status = error;
          return error;
        }).then(function (result) {
          alert("Success: " + result);
        }, function (error) {
          alert("Fail: " + error);
        })
      }
    }]);
</script>

为什么当我$scope.flag为false的时候第一个then走是error而第二个走的是success，要改的话改怎么改

Answer 1

promise.then(function (result) {
      result = result + "you have passed the first then()";
      $scope.status = result;
      // return result;
      return $q.resolve(result);
    }, function (error) {
      error = error + "failed but you have passed the first then()";
      $scope.status = error;
      // return error;
      return $q.reject(error);
    }).then(function (result) {
      alert("Success: " + result);
    }, function (error) {
      alert("Fail: " + error);
    })

Answer 2

每个.then都会返回一个新的promise。新的promise执行失败的代码后，会resolve当前传入.then的函数的返回值。因此第二个执行的是success。

这问题说多了也没用，自己看promise源码，一下就清楚了。