Making game and objects configurable for rock, paper, scissors, lizard, spock. See http://en.wikipedia.org/wiki/Rock-paper-scissors-lizard-Spock.

RPS.js

// Initializing Variables
var userChoice = prompt("Do you choose rock, paper, scissors, lizard, or spock?");
var choices = ["rock", "paper", "scissors", "lizard", "spock"];
var computerChoice = choices[ Math.floor( Math.random() * choices.length ) ];

// Function that compares the two values
function compare( choice1, choice2 ) {
    
    var rock = {
        defeats: ["scissors", "lizard"],
        loses: ["paper", "spock"],
        name: ["rock"]
    };
    
    var paper = {
        defeats: ["rock", "spock"],
        loses: ["scissors", "lizard"],
        name: ["paper"]
    };
    
    var scissors = {
        defeats: ["paper", "lizard"],
        loses: ["rock", "spock"],
        name: ["scissors"]
    };
    
    var lizard = {
        defeats: ["paper","spock"],
        loses: ["rock", "scissors"],
        name: ["lizard"]
    };
    
    var spock = {
        defeats: ["scissors", "rock"],
        loses: ["lizard", "paper"],
        name: ["spock"]
    };
    
    var perms = [rock, paper, scissors, lizard, spock];
    var plen = perms.length;
    
    for(i=0; i<plen; i++) {
        var obj = perms[i];
        if(obj.name[0] === choice1) {
            for(y=0; y<2; y++){
                switch(choice2) {
                    case obj.defeats[y]:
                        return obj.name + " defeats " + obj.defeats[y];
                        break;
                    case obj.loses[y]:
                        return obj.name + " loses to " + obj.loses[y];
                        break;
                    case obj.name[y]:
                        return obj.name + " ties " + obj.name[y];
                        break;
                }
            }
            
            // Stop looping as soon as possible.
            break;
        }
    }
}

document.write("<div>User selects: " + userChoice + "</div>");
document.write("<div>Computer selects: " + computerChoice + "</div>");
document.write("<div>Results are: " + compare(userChoice, computerChoice) + "</div>");