NodeJS - 需要模块不同步工作

Question

From what I understand after reading this question, require(ModuleName) is a synchronous operation.

In the register-rmq.js I have written the following:

const amqp = require('amqplib/callback_api');

function main(){
    return new Promise(function(resolve,reject){
      amqp.connect('localhost:5672', function(error0, connection) {
        if (error0) {
          throw error0;
        }
        connection.createChannel(function(error1, channel) {
          if (error1) {
            reject(error1);
          }
          channel.assertQueue('', {
            exclusive: true
          }, function(error2, q) {
            if (error2) {
              reject(error2);
            }
          });
          resolve(channel); //
        });
      });
    })
}

main().then(function(result){
    module.exports = {result}
})

In my controller.js I have the following two lines of code:

var channel = require('./register-rmq');
console.log(channel);

What I am expecting from the code is that the line after requiring the module in contoller.js gives me the object that I am expecting from the module which I am requiring, however the console.log that I have in controller.js gets executed before the promise gets return and therefore the channel object is empty in the controller.

Is code I have written is wrong? or Am I confused about how the operation works in this context?

Answer 1

You've already highlighted that exporting a module is done synchronously; you can't wait until a promise is resolved (or, any asyncronous operation) and expect the correct value to be exported synchronously.

The most appropriate pattern in this scenario would be the following.

register-rmq.js

module.exports = main();

controller.js

var channel = require('./register-rmq');

channel.then(result => console.log(result));