How to add a callback to a function in javascript

Question

I have two javascript functions

function one () {
   do something long... like writing jpgfile on disk
}

function two () {
   do something fast... like show         


        

Answer 1

Simple:

function one (callback) {
   do something long... like writing jpgfile on disk

    if(callback) callback();
}

function two () {
   do something fast... like show the file
}

one(two);