如何使用Node.js中异步函数返回的数据？ [英] How to use data returned by an asynchronous function in Node.js?

问题描述

我想定义一个函数，它从GET请求的响应中获取某些ID的列表：

I want to define a function that gets me a list of certain IDs from a response of a GET request:

var getList = function (){

    var list = [];

    https.get(options).on('response', function (response) {
        var body = '';
        response.on('data', function (chunk) {
            body += chunk;
        });
        response.on('end', function () {
            var obj = JSON.parse(body);
            for (i=0 ; i<obj.length ; i++){
                list.push(obj[i].id);
            }
            //console.log(list);
            //return list;
        });
    });
};

现在，我想在其他功能中使用此功能的列表，或者只是将其分配给一个变量。我明白，因为函数是异步的（好吧， https.get 一个），返回列表并不意味着其他代码不会等待这个函数完。我是否必须将所有剩余的代码放在 response.end 调用中？我知道我在这里遗漏了一些非常明显的东西......

Now, I'd like to use that list from this function in other functions or simply assign it to a variable. I understand that since the function is asynchronous (well, the https.get one), returning the list won't mean much as the other code will not wait for this function to finish. Do I have to put all the remaining code inside the response.end call? I know I'm missing something very obvious here...

推荐答案

你可以接受一个回调作为参数并调用它response.end处理程序中的相关数据：

You can accept a callback as a parameter and call it with the relevant data inside the response.end handler:

var getList = function (successCallback){

    var list = [];

    https.get(options).on('response', function (response) {
        var body = '';
        response.on('data', function (chunk) {
            body += chunk;
        });
        response.on('end', function () {
            var obj = JSON.parse(body);
            for (i=0 ; i<obj.length ; i++){
                list.push(obj[i].id);
            }

            // invoke the callback and pass the data
            successCallback(list);
        });
    });
};

然后你可以调用 getList 函数和传递回调：

Then you can call the getList function and pass in a callback:

getList(function(data) {
    // do some stuff with 'data'
});

当然其他选项是使用一些实现承诺模式以避免回调地狱。

Of course other options are to use some library implementing the Promises pattern to avoid callback hell.

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