Nodejs run task in sequence - node.js

Question

I am new to node.js and I just don't know how to execute a settimeout function before another function,
for example,
var async = require('async');
function hello(){
setTimeout(function(){
console.log('hello');
},2000);}
function world(){
console.log("world");
}
async.series([hello,world()]);
and the output is always world hello.
Am I using the library right? I dont the question seems trivial but I really have no idea how to force a short task to run after a long one

Answer 1

Async requires you to use callback. Follow this link to see some examples. The following code should output hello world correctly:
var async = require("async");
function hello(callback) {
setTimeout(function(){
console.log('hello');
callback();
}, 2000);
}
function world(callback) {
console.log("world");
callback();
}
async.series([hello, world], function (err, results) {
// results is an array of the value returned from each function
// Handling errors here
if (err) {
console.log(err);
}
});
Note that callback() was called inside the setTimeout() function so that it waits for the console.log('hello').

Answer 2

Use promise
function hello(){
return new Promise(function(resolve, reject) {
console.log('hello');
resolve();
});
}
function world(){
return new Promise(function(resolve, reject) {
console.log("world");
resolve();
});
}
hello()
.then(function(){
return world()
})
.then(function(){
console.log('both done');
})
.catch(function(err){
console.log(err);
});

Answer 3

You can use promises instead of callbacks. so your code will be something like below:
var async = require('async');
function hello(){
setTimeout(function(){
console.log('hello');
},2000);}
function world(){
console.log("world");
}
return Q.fcall(function() {
hello();
})
.then(function(resultOfHelloFunction){
world();
});
The World() function will only be executed when hello() function is completed its execution.
P.S : I am using Q library to promisify functions. It's totally fine to use other libraries (such as bluebird) to achieve the same thing.

Answer 4

You can use callback which are the heart of the nodejs.
var fun1 = function(cb){
// long task
// on done
return cb(null, result);
}
var fun2 = function(cb){
return cb(null, data);
}
fun1(function(err, result){
if(!err){
fun2(function(er, data){
// do here last task
})
}
}
// to avoid pyramid of doom use native promises
func1 (){
return new Promise((resolve, reject) => {
// do stuff here
resolve(data)
})
}
func2(){
return new Promise((resolve, reject) => {
resolve(data);
})
}
And then call them using:
func1.then((data) => {
return func2();
})
.then((resule) => {
//do here stuff when both promises are resolved
})