RPS.js

// Initializing Variables
var selection = prompt("Do you choose rock, paper or scissors?");

var PLAYS = ['scissors', 'paper', 'rock'];

var mine = PLAYS.indexOf(selection);

if(mine < 0) {
  console.log("Bad play!!");
  return;
}

var computer = Math.floor(Math.random() * 3);

var result = ((mine + 1) % 3) === computer;

if(mine === computer)
  console.log("You Tie");
else if(result)
  console.log("You Win");
else
  console.log("You Lose");

I really like the modulo.