用数学简化结果函数。 http://jsfiddle.net/afrievalt/qBbJn/

var options = ["paper", "rock", "lizard", "spock", "scissors"],
  result = [" ties ", " beats ", " loses to "],
  bigBang = function(choice1, choice2) {
      var index1 = options.indexOf(choice1), //spock => 3
          index2 = options.indexOf(choice2), //rock=> 1
          dif = index2 - index1; // 1 - 3 => -2
      if(dif < 0) { // -2 < 0 => truthy
          dif += options.length; // -2 + 5 => 3
      }
      while(dif > 2) { //3 > 2 => truthy
          dif -= 2; // 3 - 2 => 1
      }
      return choice1 + result[dif] + choice2; //spock beats rock
  };

.

  bigBang("spock", "paper");  // spock losses to paper 

  var i = Math.floor(Math.random() * 5),
      randomChoice = options[i];
  bigBang(randomChoice, userChoice);

此函数也适用于 options = ["cockroach", "nuke", "shoe"],（来自 70 年代的节目）或任何奇数长度的数组，如 options = ["water", "fire", "paper", " Rock", "tree", "metal", "mud"] //todo: 如果有任何索引 = -1，则抛出错误

让我们开始面向对象。它将减少逻辑中的重复：

//Set up the choices with what they can beat
//This is a hash table of objects you can referecne by name
var choices  =  {rock : {name: "Rock", defeats: ["scissors","lizard"]},
                 paper: {name: "Paper", defeats: ["rock", "spock"]},
                 scissors: {name: "Scissors", defeats: ["paper", "lizard"]},
                 lizard: {name: "Lizard", defeats:["paper","spock"]},
                 spock: {name: "Spock", defeats:["scissors","rock"]}
                };


//Get the computers choice
var computerChoice = Math.random();
if (computerChoice < 0.2) {
    computerChoice = "rock";
} else if (computerChoice <= 0.4) {
    computerChoice = "paper";
} else if (computerChoice <= 0.6) {
    computerChoice = "scissors";
} else if (computerChoice <= 0.8) {
    computerChoice = "lizard";
} else {
    computerChoice = "spock";
}


//Get the users choice, normalising to lower case    
var userChoice = prompt("Do you choose rock, paper, scissors, lizard, or spock?").toLowerCase();

alert("The computer chose " + computerChoice);    

//Check for a tie
if(computerChoice == userChoice){
    alert("It's a tie");
//Check for a valid choice
}else if(choices[userChoice] === undefined){
    alert("Invalid Choice");
}else{
    //Get the chosen one as an object
    userChoice = choices[userChoice];



    //Check For a win
    /*var victory = false;
    for(var i = 0; i < userChoice.defeats.length; i++){
        if(computerChoice == userChoice.defeats[i])
        {
            victory = true;
            break;
        }
    }*/

    //Improved check, inspired by Mke Spa Guy
    var victory = userChoice.defeats.indexOf(computerChoice) > -1;

    //Display result
    if(victory) {
        alert("Vitory! " + userChoice.name + " wins!")
    }else{
        alert("Defeat, " + computerChoice + " wins!");
    }   
}

就是这样，Spocks 是你的叔叔。

演示

完整动作演示：例如：Paper Covers Rock；

更多阅读：

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Introduction_to_Object-Oriented_JavaScript

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Working_with_Objects

http://www.mojavelinux.com/articles/javascript_hashes.html

我会编写一个函数来获得正确的响应，而不是全部内联……这就是我……

function getUserChoice(){
    var invalidPin = true;
    var response;
    while(invalidPin){
        response = prompt("choose your thing..");
            if(response == "rock" || response == "paper" || response == "scizerz"){
                invalidPin = false;
            }
        }
    }
    return response;
}

那么您只需调用该函数即可获得用户的选择

var userChoice = getUserChoice();

正如一些用户所提到的，比较的最佳选择是将输入转换为小写。

对于您的第二点，我会将输入解析包装在一个循环中，如下所示：

while(true){
    var input = getInput();

    if(isValid(input)){
        // check for the winner
        break;
    }else{
        // tell the user that their input is invalid
    }
}

我会做类似以下的事情（请注意，语法可能会稍微偏离）：

var compare = function (choice1, choice2)
{
    switch (choice1.tolower())
    {
        case "rock"
            RockPicked(choice2);
            break;
        case "scissors"
            ScissorsPicked(choice2);
            break;
        ....
        ....
        case default
            alert ("Selection was invalid")
            break;
    }

}

// if the user picked rock then we compare the computers choice and decide winner
var RockPicked = function(choice2)
{
    if (choice2 === "scissors") 
    {
        alert("Rock wins!");
    } 
    else if (choice2 === "paper") 
    {
        alert("Paper wins!");
    } 
    else if (choice2 === "lizard") 
    {
        alert("Rock wins!");
    } 
    else 
    {
        alert("Spock wins!");
    }
}