how to wait the end of the execution of a function - node.js

Question

I have a main in nodejs for my program where I need to use my result calculated in a module, but my I don't have the right result.
var myJSONClient = {
"nombre" : "<nombre_cliente>",
"intervalo" : [0,0]
};
var intervalo = gestionar.gestion(myJSONClient,vector_intervalo);
console.log("intervalo: "+intervalo); //return undefined
And this is the module
var gestion = function(myJSON,vector_intervalo) {
var dburl = 'localhost/mongoapp';
var collection = ['clientes'];
var db = require('mongojs').connect(dburl, collection );
var intervalo_final;
function cliente(nombre, intervalo){
this.nombre = nombre;
this.intervalo = intervalo;
}
var cliente1 = new cliente(myJSON.nombre,myJSON.intervalo);
db.clientes.save(cliente1, function(err, saveCliente){
if (err || !saveCliente) console.log("Client "+cliente1.nombre+" not saved Error: "+err);
else {
console.log("Client "+saveCliente.nombre+" saved");
intervalo_final = calculate(vector_intervalo);
console.log(intervalo_final); //here I can see the right content of the variable intervalo_final
}
});
setTimeout(function(){
console.log("pause");
},3000);
console.log(intervalo_final); //result not correct
return intervalo_final;
}
exports.gestion = gestion;
I know that node execute my return without wait the end of my function, for this I can't see the right result, but how can I force my program to wait the end of my function?
I tried with the setTimeout function but wasn't the right way.

Answer 1

You must implement your function just like the other async functions from the API!
First step : give callback to function
var gestion = function(myJSON,vector_intervalo, callback) {
Second step : when the async process is over call callback passing the result (you don't need the return line)
console.log(intervalo_final); //here I can see...
callback(intervalo_final);
Step three: use your function in an async way
gestionar.gestion(myJSONClient,vector_intervalo, function(result){
console.log(result);
});

Answer 2

In async JS you can't return a value the way it seems you trying to do. You need to pass a callback function from your main program when calling gestionar.gestion() (you can add it as a third argument).
Your code sample won't work because function gestion() returns immediately, before intervalo_final content is set.
Something like this:
gestionar.gestion(myJSONClient,vector_intervalo, function callback(intervalo) {
// This is the callback function
console.log("intervalo: " + intervalo);
});
And then within the function:
var gestion = function(myJSON,vector_intervalo, callback) {
...
db.clientes.save(cliente1, function(err, saveCliente) {
if (err || !saveCliente) {
console.log("Client "+cliente1.nombre+" not saved Error: "+err);
if (callback) callback(); // execute callback function without arguments
}
else {
console.log("Client "+saveCliente.nombre+" saved");
intervalo_final = calculate(vector_intervalo);
console.log(intervalo_final);
if (callback) callback(intervalo_final); // your callback function will be executed with intervalo_final as argument
}
});
Also, I highly recommend reading some async javascript tutorial, like http://javascriptissexy.com/understand-javascript-callback-functions-and-use-them/
And Felix's Node.js Guide: http://nodeguide.com/