Question

55

Simplest way to wait some asynchronous tasks complete, in Javascript?

rated 0 times [ 56] [ 1] / answers: 1 / hits: 184512 / 12 Years ago, fri, may 11, 2012, 12:00:00

I want to drop some mongodb collections, but that's an asynchronous task. The code will be:

var mongoose = require('mongoose');



mongoose.connect('mongo://localhost/xxx');



var conn = mongoose.connection;



['aaa','bbb','ccc'].forEach(function(name){

    conn.collection(name).drop(function(err) {

        console.log('dropped');

    });

});

console.log('all dropped');

The console displays:

all dropped

dropped

dropped

dropped

What is the simplest way to make sure all dropped will be printed after all collections has been dropped? Any 3rd-party can be used to simplify the code.

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lailab

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answered 12 Years ago osvaldo · Accepted Answer

I see you are using mongoose so you are talking about server-side JavaScript. In that case I advice looking at async module and use async.parallel(...). You will find this module really helpful - it was developed to solve the problem you are struggling with. Your code may look like this

var async = require('async');



var calls = [];



['aaa','bbb','ccc'].forEach(function(name){

    calls.push(function(callback) {

        conn.collection(name).drop(function(err) {

            if (err)

                return callback(err);

            console.log('dropped');

            callback(null, name);

        });

    }

)});



async.parallel(calls, function(err, result) {

    /* this code will run after all calls finished the job or

       when any of the calls passes an error */

    if (err)

        return console.log(err);

    console.log(result);

});