A short example of callback hell.

cat-example2.js

getCat((data) => {
  const catEmbed = new RichEmbed({ title: 'Meow' })
  catEmbed.setImage(data.file);
  message.channel.send("Nyaa ~ :cat: ", { embed: catEmbed })
    .then(message => console.log(`Sent message: ${message.content}`))
    .catch(console.error);
  /* ES5 Function */
  getCat(function (data) {
    /* Cat data 2 operations... */
    getCat((data) => {
      /* Cat data 3 operations... */
      getCat((data) => {
        /* Cat data 4 operations... 
        * Okay, too many callbacks now.
        * Oh look a triangle.
        */
      });
    });
  });
  
});