如何链接多个条件承诺? [英] How do I chain multiple conditional promises?

问题描述

在我的代码中，我有条件任务，所有任务都返回承诺.我需要任务按顺序运行.

我当前的实现看起来像这样:

  var链= [];if(/*任务A的某些条件*/){chain.push(function(doContinue){taskA().then(doContinue);});}if(/*任务B的某些条件*/){chain.push(function(doContinue){taskB().then(doContinue);});}if(/*任务C的某些条件*/){chain.push(function(doContinue){taskC().then(doContinue);});}var processChain = function(){如果(chain.length){chain.shift()(processChain);} 别的 {console.log(完成所有任务");}};processChain(); 

这很好用，但是最初我正在寻找一种仅使用Promises创建链并使用 .then 链接所有函数的方法，但是我没有一个可行的解决方案./p>

如果有一种更简洁的方法，仅使用Promises和 then 调用链，那么我想看看一个例子.

解决方案

一种可能的方法:

  var promiseChain = Promise.resolve();如果(shouldAddA)promiseChain = promiseChain.then(taskA);如果(shouldAddB)promiseChain = promiseChain.then(taskB);如果(shouldAddC)promiseChain = promiseChain.then(taskC);返回promiseChain; 

另一个:

 返回Promise.resolve().then(shouldAddA&& taskA).then(shouldAddB&& taskB).then(应该AddC&& taskC); 

In my code I have conditional tasks, which all return a promise. I need the tasks to run in sequence.

My current implementation looks something like this:

var chain = [];

if (/* some condition for task A */) {
    chain.push(function(doContinue){
        taskA().then(doContinue);
    });
}

if (/* some condition for task B */) {
    chain.push(function(doContinue){
        taskB().then(doContinue);
    });
}

if (/* some condition for task C */) {
    chain.push(function(doContinue){
        taskC().then(doContinue);
    });
}

var processChain = function () {
    if (chain.length) {
        chain.shift()(processChain);
    } else {
        console.log("all tasks done");
    }
};

processChain();

This works fine, but initially I was looking for a way to create the chain using only Promises and chaining all functions using .then, but I wasn't able to get a working solution.

If there's a cleaner way using only Promises and chains of then calls, then I'd love to see an example.

解决方案

One possible approach:

var promiseChain = Promise.resolve();
if (shouldAddA) promiseChain = promiseChain.then(taskA);
if (shouldAddB) promiseChain = promiseChain.then(taskB);
if (shouldAddC) promiseChain = promiseChain.then(taskC);
return promiseChain;

Another one:

return Promise.resolve()
  .then(shouldAddA && taskA)
  .then(shouldAddB && taskB)
  .then(shouldAddC && taskC);

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