node.js - 如何控制以下代码片段的 Node.js 的异步性质

Question

我们如何实现以下代码片段的同步代码。我们要在前一个函数的回调函数中编写代码。这创造了回调 hell (正如他们所说)。如何分别编写男性和女性分别读取记录并且可以同步执行。我们如何保留 console.log(id[0]); 的值在 for 循环中。如果我的方向错误，请纠正我。

var male_arr = []; var female_arr = [];

/*************   Fetching record from database with condition gender=0
***************/ user.find({gender: 0}, {_id: 1}, function (err_male, male) {

    if (err_male) {
        console.log(err_male);
    }

    male_arr = male;    // initializing males array
    looplength = male.length;
    //
    // With CAALBACK function, we have fetched records with condition gender = 1
    //
    user.find({gender: 1}, {_id: 1}, function (err_female, female) {
        if (err_female) {
            console.log(err_female);
        }

        female_arr = female;     // initializing females array

            // Populate the male array
            for (var loop = 0; loop < looplength; loop++) {

                var id = male_arr.splice(0, 1);
     //#1          /*****here is the spliced element********/

                console.log("Outside request api");
                console.log(id[0]);


                // Get all records of females which are in request table of male at id[0]
                request.find({male: id[0]._id}, {female: 1}, function (err, data) {
    //#2           /*****This value of male in id[0] is not retained for match ********/
                    console.log("Inside request api");
                    console.log(id[0]);
                    if (err) {
                        console.log(err);
                    }
                });

            }

    }); });

Answer 1

虽然 Caio 的答案可能适合您的问题，但我可以建议使用 Promises 吗？

使用Bluebird你可以这样做:

Note: this is an example and it might not be actually functional.

var Promise = require('bluebird');

var getMaleFn() {
    return new Promise(function(resolve, reject){
        // Make the call to your API.
        // Handle errors, if any, return reject(err);
        return resolve(males);
    });
}

var getFemaleFn() {
    return new Promise(function(resolve, reject){
        // Make the call to your API.
        // Handle errors, if any, return reject(err);
        return resolve(females);
    });
}

var males = [];
var females = [];

// Fetch all males
getMaleFn()
    //Iterate each male and put it in the array
    .map(function(male) {
        males.push(male);
    })
    // Fetch all females
    .then(function(){
        return getFemaleFn()
    })
    //Iterate each females and put it in the array
    .map(function(female) {
        females.push(female);
    })
    .then(function(){
        console.log('done!');
    });