Callbacks are rampant in Javascript, this can cause what's known as "Callback Hell", or as I like to call. Rat nests. In the following example the "rat nest" is not that hard to follow along with, and that will be the case when your program is simple. But imagine when your program grows to have many rat nests, perhaps even the rat nests become intertwined. Messy.
/*
* Callback hell example
*/
function yell(text, callback) {