Is return will work fine in node.js in normal functions without IO Operations?

My function is like this for examle

function summ(a,b)
{
 return a+b;
}

module.exports.summ = summ;

in other file:

var obj = require('./that file')

function app()
{
 var s = obj.summ(7,7);
}

if i put console.log(s); it is giving answer perfect. My doubt is this will come all the time when request is coming frequently since i m using this kind of return in rest api ? Or call back function is required like that result is

function summ(a,b,callback)
{
 callback(a+b);
}

and

function app()
{
 obj.summ(7,7,function(result){
 var s = result;
  }
 }