JavaScript：while循环中的异步方法

问题描述

我正在处理一个项目，该项目要求我在API方法调用中使用JavaScript。我是一名Java程序员，之前从未进行过web开发，所以我遇到了一些麻烦。

I'm tackling a project that requires me to use JavaScript with an API method call. I'm a Java programmer who has never done web development before so I'm having some trouble with it.

这个API方法是异步的，它在while循环中。如果它返回一个空数组，则while循环结束。否则，它循环。代码：

This API method is asynchronous and it's in a while loop. If it returns an empty array, the while loop finishes. Otherwise, it loops. Code:

var done = true;

do
{
    async_api_call(
        "method.name",
        {
            // Do stuff.
        },
        function(result)
        {
            if(result.error())
            {
                console.error(result.error());
            }
            else
            {
                // Sets the boolean to true if the returned array is empty, or false otherwise.
                done = (result.data().length === 0) ? true : false;
            }
        }
    );

} while (!done);

这不起作用。循环在完成的值更新之前结束。我已经完成了一些关于这个主题的阅读，看起来我需要使用promises或回调，因为API调用是异步的，但我无法理解如何将它们应用到我上面的代码中。

This doesn't work. The loop ends before the value of "done" is updated. I've done some reading up on the subject and it appears I need to use promises or callbacks because the API call is asynchronous, but I can't understand how to apply them to the code I have above.

帮助将不胜感激！

推荐答案

编辑：底部，有真正的答案。

我鼓励你使用。您的问题可以使用 Promise.all 来解决：

edit: see the bottom, there is the real answer.

I encourage you yo use the Promise API. Your problem can be solved using a Promise.all call:

let promises = [];
while(something){
    promises.push(new Promise((r, j) => {
        YourAsyncCall(() => r());
    });
}
//Then this returns a promise that will resolve when ALL are so.
Promise.all(promises).then(() => {
    //All operations done
});

语法在es6中，这里是es5等价的（Promise API可能包含在外部）：

The syntax is in es6, here is the es5 equivalent (Promise API may be included externally):

var promises = [];
while(something){
    promises.push(new Promise(function(r, j){
        YourAsyncCall(function(){ r(); });
    });
}
//Then this returns a promise that will resolve when ALL are so.
Promise.all(promises).then(function(){
    //All operations done
});

您也可以让api调用返回承诺并将其直接推送到promise数组。

You can also make your api call return the promise and push it directly to the promise array.

如果你不想编辑 api_call_method ，你可以随时将你的代码包装成一个新的专业版mise并在完成后调用方法解决。

If you don't want to edit the api_call_method you can always wrap your code in a new promise and call the method resolve when it finishes.

编辑：我现在已经看到了代码的重点，对不起。我刚刚意识到Promise.all不会解决问题。

edit: I have seen now the point of your code, sorry. I've just realized that Promise.all will not solve the problem.

你应该把你发布的内容（不包括while循环和控制值）放在一个函数中，并根据调用它的条件。

You shall put what you posted (excluding the while loop and the control value) inside a function, and depending on the condition calling it again.

然后，所有都可以包含在promise中，以使外部代码知道此异步执行。我稍后会用我的电脑发布一些示例代码。

Then, all can be wraped inside a promise in order to make the external code aware of this asynchronous execution. I'll post some sample code later with my PC.

你可以用一个承诺控制应用程序的流程并使用递归而不是while循环：

You can use a promise to control the flow of your application and use recursion instead of the while loop:

function asyncOp(resolve, reject) {
    //If you're using NodeJS you can use Es6 syntax:
    async_api_call("method.name", {}, (result) => {
      if(result.error()) {
          console.error(result.error());
          reject(result.error()); //You can reject the promise, this is optional.
      } else {
          //If your operation succeeds, resolve the promise and don't call again.
          if (result.data().length === 0) {
              asyncOp(resolve); //Try again
          } else {
              resolve(result); //Resolve the promise, pass the result.
          }
      }
   });
}

new Promise((r, j) => {
    asyncOp(r, j);
}).then((result) => {
    //This will call if your algorithm succeeds!
});

/*
 * Please note that "(...) => {}" equivals to "function(...){}"
 */

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