取消承诺链? [英] Cancel a promise chain?

问题描述

我兑现了一系列承诺:

this.getData.then(this.getMoreData).then(this.getEvenMoreData);

在某个时候，用户可能决定取消该请求并请求其他请求.

At some point the user may decide to cancel the request and request something else.

如何取消链条的传播?

推荐答案

您必须检查每个链接方法中的状态(是否应该取消):

You'd have to check for the state (of whether you should cancel or not) inside each chained method:

var userRequestedCancel = false;

this
   .getData()
   .then(function() {
     if(userRequestedCancel) {
      return Promise.reject('user cancelled');
     }

     return getMoreData();
   })
   .then(function() {
     if(userRequestedCancel) {
      return Promise.reject('user cancelled');
     }

     return getEvenMoreData();
   })

或者也许是一种稍微更优雅的方式(已编辑为将上下文和参数传递给callback方法)

Or perhaps a slightly more elegant way (edited to pass context and arguments to callback methods)

var currentReq = false;
var userRequestedCancel = false;
var shouldContinue = function(cb,args) {
    if(userRequestedCancel) {
        return Promise.reject('user cancelled');
    }

    currentReq = cb.apply(this,args);
    return currentReq;
}

var onCancel = function() {
    userRequestedCancel = true;
    currentReq && currentReq.abort();
}

this
   .getData()
   .then(function() {
    return shouldContinue(getMoreData,arguments);
   })
   .then(function() {
     return shouldContinue(getEvenMoreData,arguments);
   })

如果您还需要取消当前请求(这很简单)，请将当前的ajax请求设置为全局变量，并且无论将userRequestedCancel标志设置为true的哪个事件，也都可以取消ajax请求(请参见上面的编辑代码)

If you need to cancel the current request as well, that is kind of trivial, set your current ajax request to be a global variable, and whatever event sets the userRequestedCancel flag to true, have that also cancel the ajax request (see edited code above)

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