你如何阻止一个 promise then 函数进入下一个 then 函数？ [复制]答案

【问题标题】：How do you stop a promise then function from going onto the next then function? [duplicate]你如何阻止一个 promise then 函数进入下一个 then 函数？ [复制]
【发布时间】：2016-09-25 17:58:05
【问题描述】：

我是 Promise 的新手，我觉得这应该是一件非常简单的事情。

如果变量返回 true，我希望下面的代码在第一个 then 处停止：

           if (groupCodes.length === 1) {
                // Get all does not populate the group object so it will just be the identifier as we require
                var groupIdentifier = groupCodes[0].group;

                GroupMember
                .nestedCreate({ groupId: groupIdentifier, type: groupCodes[0].type }, { })
                .$promise
                .then(function (group) {
                    var isUserAlreadyInGroup = _.includes(group, user._id);
                    if (isUserAlreadyInGroup) {
                        // If this variable returns true I would like to preent the below then function from running
                        notify.info('You have already joined ' + scope.groupCode);
                    }
                })
                .then(function () {
                    // Now that we have joined the group, we have permission
                    // to access the group data.
                    return Group
                        .getById({ groupId: groupIdentifier })
                        .$promise;
                })
           }

【问题讨论】：

从第一个 then 方法返回一个值。在第二个then 中询问该值以确定您是否应该继续。
你用什么来兑现承诺？
问的问题实际上是一个骗子，但这种情况下的解决方案比复杂的承诺炼金术要简单得多......只需将两个函数合并 if- else 语句

标签： javascript

【解决方案1】：

试试这个：

if (groupCodes.length === 1) {
    // Get all does not populate the group object so it will just be the identifier as we require
    var groupIdentifier = groupCodes[0].group;

    GroupMember
     .nestedCreate({ groupId: groupIdentifier, type: groupCodes[0].type }, { })
     .$promise
     .then(function (group) {
         var isUserAlreadyInGroup = _.includes(group, user._id);
         if (isUserAlreadyInGroup) {
             // If this variable returns true I would like to preent the below then function from running
             notify.info('You have already joined ' + scope.groupCode);
         }

         return isUserAlreadyInGroup;
     })
     .then(function (isUserAlreadyInGroup) {
         if (!isUserAlreadyInGroup) {
             // Now that we have joined the group, we have permission
             // to access the group data.
             return Group
              .getById({ groupId: groupIdentifier })
              .$promise;
             });
         })
     }

【讨论】：

【解决方案2】：

根据您对我的问题的回答，如果您使用的 Promise 库无法提供您想要的方式，您始终可以让第二个 then 成为一个单独的函数，有条件地从第一个then 函数。

首先，将第二个then 定义为单独的函数。

var secondThen = function(groupIdentifier) {
  // Now that we have joined the group, we have permission
  // to access the group data.
  return Group
    .getById({
      groupId: groupIdentifier
    })
    .$promise;
};

这是您示例中的then sn-p，使用我的建议。

.then(function(group) {
    var isUserAlreadyInGroup = _.includes(group, user._id);
    if (isUserAlreadyInGroup) {
      notify.info('You have already joined ' + scope.groupCode);
    } else {
      // I'm not sure where `groupIdentifier` comes from, I assume you can figure that out, since you had it in your code
      secondThen(groupIdentifier);
    }
})

【讨论】：