node.js - nodejs中module.export为一个异步返回结果时该怎么做?

Answer 1

Your implementation is a bit strange. I think the following is more suitable.

a.js

var MongoClient = require('mongodb').MongoClient;


var main = {
  getResult: function(callback) {
    MongoClient.connect('mongodb://localhost:27017/local', function(err, db) {

      // Use the admin database for the operation
      var adminDb = db.admin();
      // List all the available databases
      adminDb.listDatabases().then(function(dbs) {
        var result = [];
        dbs.databases.forEach(function(element, index) {
          result.push(element.name);
        })
        db.close();
        callback(result);
      });
    });
  }
};

module.exports = main;

b.js:

var a = require("./a");

a.getResult(function(result){
  console.log(result);
});

In addition, require js files do not need to have a .js extension. If you want to write asynchronously using promises instead of callbacks, please refer to bluebird.

Answer 2

Why is module.exports placed in the then callback function?
You must know that the main logic of a.js is executed asynchronously~~~

var data = require("a.js");
console.log(data); 

Recommendations:
1) Export function module
2) The export module inherits EventEmitter
3) After the promise function is executed, send event notification
4) Listen where the module is imported Notification of this event