random.js

// Store an array of strings with each choice
var choices = [
  'rock',
  'paper',
  'scissors'
];

// Store an array of strings with each image URL
var images = [
  'http://i.imgur.com/n6xptEr.png',
  'http://i.imgur.com/n4bDRXp.png',
  'http://i.imgur.com/E7loAXb.png'
];

// Pick a random number between 1 and 3
var randomIndex = Math.floor(Math.random() * 3)

// Use the randomIndex to pick a choice
var computerChoice = choices[randomIndex];

// Use the same index to pick the right image from the array
var computerChoiceImage = images[randomIndex];