使得异步在一个循环中的JavaScript任务 [英] Making async javascript task in a loop

问题描述

function(obj){
for (property in obj) {
 if (obj.hasOwnProperty(property)) {
    // some code here
   if(condition){
    obj.children = example.getdata(base, obj.name);
     }
  // some more code releated to obj
   }
 }
if (obj.length == 10)
 {
  //some more function
 }
}

现在我想要的 example.getdata 异步，但我不希望执行如果语句中的循环，直到所有的同步之后任务都做了。
它更多的像我希望所有的 example.getdata 函数调用来并行执行和他们完成工作后，我执行，如果（obj.length）。

Now i want to make example.getdata async but i dont want to execute if statement that is after for loop until all the sync tasks are done. Its more of like i want all the example.getdata function calls to execute in parallel and after they finish work i execute if (obj.length).

我尝试使用的承诺，推动所有承诺并加以解决，但我不知道如何来处理每个函数调用的返回值。

I tried using promises and push all the promises and resolve them but i dont know how to handle the return value for each function call.

推荐答案

下面是一个使用循环许诺干净的例子。如果你能挑一个承诺库库像蓝鸟将使它更简单：

Here is a clean example of a for loop using promises. If you can pick a promise library libraries like Bluebird will make it even simpler:

function(obj){

  var props = Object.keys(obj), p = Promise.resolve();
  props.forEach(function(prop){
    p = p.then(function(){
      if(condition){ // can access obj[prop] and obj here
        obj.children = example.getData(...); // getData returns a promise
        return obj.children; // return the promise.
      }
    });
});

Promise.resolve(obj.children).then(function(children){
    // here the async call to get `.children` is done.
    // can wait for `p` too (the loop) if we care about it
    if(obj.length === 10) // do stuff
});

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