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

You only need to use a callback if you are doing something asynchronous, otherwise it doesn't matter how long something takes, the next function won't run until the first has finished.

A callback is just passing a function as an argument, and then calling it when done.

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

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

one(two);

Obviously, if you are doing something asynchronous, then you need something that will tell you when it is finished (such as an event firing).