I'm working on making my first game (Rock Paper Sissors) and I ran into an issue where when the userChoice is scissors and the computerChoice is rock, the program cannot return the winner as rock. I can get the program to give me the winner for any other combination.

I have my code here:

var userChoice = prompt("Do you choose rock, paper or scissors?");
var computerChoice = Math.random();
if (computerChoice < 0.34) {
    computerChoice = "rock";
} else if(computerChoice <= 0.67) {
    computerChoice = "paper";
} else {
    computerChoice = "scissors";
}

var compare = function(choice1, choice2) {
    if(choice1 === choice2) {
    return "The result is a tie!";
}
if(choice1 === "rock") {
    if(choice2 === "scissors") {
        return "rock wins";
    } else {
        return "paper wins";
    }
}
if(choice1 === "paper") {
    if(choice2 === "rock") {
        return "paper wins";
    } else {
        if(choice2 === "scissors") {
            return "scissors wins";
    }
}
if(choice1 === "scissors") {
    if(choice2 === "rock") {
        return "rock wins";
    } else {
        if(choice2 === "paper") {
            return "scissors wins";
        }
    }
}
}
};
console.log("User Choice: " + userChoice);
console.log("Computer Choice: " + computerChoice);
compare(userChoice, computerChoice);

I'm working on making my first game (Rock Paper Sissors) and I ran into an issue where when the userChoice is scissors and the computerChoice is rock, the program cannot return the winner as rock. I can get the program to give me the winner for any other combination.

I have my code here:

var userChoice = prompt("Do you choose rock, paper or scissors?");
var computerChoice = Math.random();
if (computerChoice < 0.34) {
    computerChoice = "rock";
} else if(computerChoice <= 0.67) {
    computerChoice = "paper";
} else {
    computerChoice = "scissors";
}

var compare = function(choice1, choice2) {
    if(choice1 === choice2) {
    return "The result is a tie!";
}
if(choice1 === "rock") {
    if(choice2 === "scissors") {
        return "rock wins";
    } else {
        return "paper wins";
    }
}
if(choice1 === "paper") {
    if(choice2 === "rock") {
        return "paper wins";
    } else {
        if(choice2 === "scissors") {
            return "scissors wins";
    }
}
if(choice1 === "scissors") {
    if(choice2 === "rock") {
        return "rock wins";
    } else {
        if(choice2 === "paper") {
            return "scissors wins";
        }
    }
}
}
};
console.log("User Choice: " + userChoice);
console.log("Computer Choice: " + computerChoice);
compare(userChoice, computerChoice);

• javascript

• There was a syntax error missing required brace or something at the end of the function, and you inserted it there? Don't believe them, the brace was missing somewhere else but the parser did recognice that at the end. – Bergi Commented Jul 31, 2013 at 17:26
• 2 This code, once fixed, should be sent to Code Review, it can be optimized by a lot. – Jeff Noel Commented Jul 31, 2013 at 17:28
• 1 they solved your problem. but you should be using "else if" when its appropriate like in your code.. also do you really need all those {} ? cleaner code has less mistakes – gezzuzz Commented Jul 31, 2013 at 17:31
• @gezzuzz, I'm not sure if I need all of the {}... I just started learning JavaScript two days ago at Codecademy. Could you show me a working example without all of the braces? – Godzdude Commented Jul 31, 2013 at 17:51

14 Answers 14

Something to study:

var choices = ["rock", "paper", "scissors"];
var map = {};

choices.forEach(function(choice, i) {
    map[choice] = {};
    map[choice][choice] = "Was a tie"
    map[choice][choices[(i+1)%3]] = choices[(i+1)%3] + " wins"
    map[choice][choices[(i+2)%3]] = choice + " wins"
})

function compare(choice1, choice2) {
    return (map[choice1] || {})[choice2] || "Invalid choice";
}

Here's an alternate that will work for expanded sets. The assumption is that there's an odd number of possibilities, and from any given point, of the total number of opposition, reading forward from our given point (and wrapping around when we reach the end) the first half will win over the given point, and the second half will lose.

Or another way to describe it would be that the half of the remaining opponents that precede our given point will lose, and the half that follow will win.

Therefore the proper order in the choices Array is crucial.

var choices = ["rock", "spock", "paper", "lizard", "scissors"];
var map = {};

choices.forEach(function(choice, i) {
    map[choice] = {};
    for (var j = 0, half = (choices.length-1)/2; j < choices.length; j++) {
        var opposition = (i+j)%choices.length
        if (!j)
            map[choice][choice] = "Was a tie"
        else if (j <= half)
            map[choice][choices[opposition]] = choices[opposition] + " wins"
        else
            map[choice][choices[opposition]] = choice + " wins"
    }
})

function compare(choice1, choice2) {
    return (map[choice1] || {})[choice2] || "Invalid choice";
}

You were unable to see the issue most likely due to poor indentation of your code. Properly indented the issue is clear:

if (choice1 === "paper") {
    if (choice2 === "rock") {
        return "paper wins";
    } else {
        if (choice2 === "scissors") {
            return "scissors wins";
        }
    }
    if (choice1 === "scissors") {
        if (choice2 === "rock") {
            return "rock wins";
        } else {
            if (choice2 === "paper") {
                return "scissors wins";
            }
        }
    }
}

Your if (choice1 === "scissors") { is within if (choice1 === "paper") {. The code within will never be reached.

I came up with an alternative that should be easy for you to understand and avoids some issues in your code, like excessive repetition and fixed choices. It is thus much more flexible and easier to maintain.

function compare(choice1, choice2) {
    choice1 = choices.indexOf(choice1);
    choice2 = choices.indexOf(choice2);
    if (choice1 == choice2) {
        return "Tie";
    }
    if (choice1 == choices.length - 1 && choice2 == 0) {
        return "Right wins";
    }
    if (choice2 == choices.length - 1 && choice1 == 0) {
        return "Left wins";
    }
    if (choice1 > choice2) {
        return "Left wins";
    } else {
        return "Right wins";
    }
}

choices is var choices = ["rock", "paper", "scissors"];. You can see a demonstration.

To generalize the solution to larger lists, this modulo technique can be helpful:

function mod(a, b) {
    c = a % b
    return (c < 0) ? c + b : c
}

Then it's much easier to write the comparison code:

function compare(choice1, choice2) {
    x = choices.indexOf(choice1);
    y = choices.indexOf(choice2);
    if (x == y) {
        return "Tie";
    }
    if (mod((x - y), choices.length) < choices.length / 2) {
        return choice1 + " wins";
    } else {
        return choice2 + " wins";
    }
}

The corresponding jsFiddle.

So many if statements. They are confusing.

Also, all those if statements lock in the game and make it hard to reuse the logic for another game.

function referee(){
    var training = {};
    function learn(winner,loser){
        if (!training[winner]) training[winner] = {};
        training[winner][loser]=1;
    }
    function judge(play1,play2){
        if (play1 === play2){ return 'tie'; }
        return ( (training[play1][play2] === 1)? play1: play2 )+' wins!';
    }
    function validate(choice) {
        return choice in training;
    }
    function choices() {
        return Object.keys(training);
    }
    return {
        'learn': learn,
        'judge': judge,
        'validAction': validate,
        'getChoices': choices
    };
}

var ref = referee();
ref.learn('rock','scissors');
ref.learn('paper','rock');
ref.learn('scissors','paper');

do {
    var userChoice = prompt("Do you choose rock, paper or scissors?");
} while(!ref.validAction(userChoice))
var choices = ref.getChoices(),
    computerChoice = choices[Math.floor(Math.random()*choices.length)];

console.log("User Choice: " + userChoice);
console.log("Computer Choice: " + computerChoice);
console.log(ref.judge(userChoice, computerChoice));

You have a mismatched brace:

if(choice1 === "paper") {
    if(choice2 === "rock") {
        return "paper wins";
    } else {
        if(choice2 === "scissors") {
            return "scissors wins";
    }
}

I'd actually remove the last if in that block, you don't need it. The last block (choice1 === "scissors") is correct, but again the last if is not required.

To show you why it's failing in that particular way, I have re-indented the relevant part of your code to illustrate how it is being interpreted:

if(choice1 === "paper") {
    if(choice2 === "rock") {
        return "paper wins";
    } else {
        if(choice2 === "scissors") {
            return "scissors wins";
        }
    }
    if(choice1 === "scissors") {
        if(choice2 === "rock") {
            return "rock wins";
        } else {
            if(choice2 === "paper") {
                return "scissors wins";
            }
        }
    }
}

Try This :

var UserChoice = window.prompt("Do you choose rock, paper or scissors ?");

var computChoice = Math.random();

var computChoice = computChoice < 0.34 ? "rock" : ( computChoice > 0.67 ? "scissors" : "paper" ) ;

var mess = { 
  rock : { scissors : 'You Win!, Rock smashes scissors!', paper : 'You lose!, Paper covers rock!'} ,
  paper : { rock : 'You Win!, Paper covers rock!', scissors : 'You lose!, Scissors cut paper!' },
  scissors : { paper : 'You Win!, Scissors cut paper!', rock : 'You lose!, Rock smashes scissors!' }
}

if ( computChoice === UserChoice)
  result = "It's a tie!" ; 
	 
else if ( UserChoice !== "rock" && UserChoice !== "paper" && UserChoice !== "scissors" )
  result = "Invalid choice! Choose from rock, paper, or scissors" ;

else
  result = mess[UserChoice][computChoice] ;

console.log( 'you chose ' + UserChoice + ' and computer chose ' + computChoice + ' ( ' + result + ' ) ') ;

This is how I did mine:

    //player choice
    var playerChoice = prompt("What is your choice of weapon: rock, paper, or scissors?");
    
    //Computer Choice
    var computerChoice = Math.ceil(Math.random() *3);
    
    //variables as numbers
    if (computerChoice < 1) {
        computerChoice = "rock";
    } else if(1 <= computerChoice <= 2) {
        computerChoice = "paper";
    } else {
        computerChoice = "scissors";
    }
    
    
    //defining function
    function game(playerChoice, computerChoice){
    
    //Checking for a tie
    if (playerChoice === computerChoice) {
          return "It is a tie";
        }
    
        //Check for Rock
        if (playerChoice === "rock") {
          if (computerChoice === "scissors") {
            return "Player Wins";
          } else {
            return "Computer Wins";
          }
        }
        //Check for Paper
        if (playerChoice === "paper") {
          if (computerChoice === "scissors") {
            return "Computer Wins";
          } else {
            return "Player Wins";
          }
        }
        //Check for Scissors
        if (playerChoice === "scissors") {
          if (computerChoice === "rock") {
            return "Computer Wins";
          } else {
                    return "Player Wins";
          }
        }
    }
    
    //start the game function
    game();
    //print winner
    console.log(game(playerChoice, computerChoice))

I chose to have my computerChoice be random, whole number, 0-3, but you can take that part out.

I got this to work:

function playFunction() {
var userChoice = prompt("Do you choose rock, paper or scissors?");
var computerChoice = Math.random();
if (computerChoice < 0.34) {
    computerChoice = "rock";
} else if(computerChoice <= 0.67) {
    computerChoice = "paper";
} else {
    computerChoice = "scissors";
}

var compare = function(choice1, choice2) {
    if(choice1 === choice2) {
      alert("The result is a tie!");
}
if(choice1 === "rock") {
    if(choice2 === "scissors") {
        alert("rock wins");
    } else {
        alert("paper wins");
    }
}
if(choice1 === "paper") {
    if(choice2 === "rock") {
        alert("paper wins");
    } else {
        if(choice2 === "scissors") {
            alert("scissors wins");
    }
}
if(choice1 === "scissors") {
    if(choice2 === "rock") {
        alert("rock wins");
    } else {
        if(choice2 === "paper") {
           alert("scissors wins");
        }
    }
}
}
};
console.log("User Choice: " + userChoice);
console.log("Computer Choice: " + computerChoice);
compare(userChoice, computerChoice)
} 

All I changed was instead of returning a message, it pops up an alert with the answer. I also put it into one function that could be called on an HTML button click.

Example without all the {} and else if

always use else if when you can.. since your if statements are different cases and only one applies you should use else if..

with if statements if you only have 1 statement after the condition you don't need {} (condition 1 below).. even if you have a if.. else if...block statement its considered one statement..(condition 2 below).. but if it helps you can use them around the if.. else if...block statement to help your understand it better ..(condition 3 below).. ..

also don't use === unless you really know what it does.. it can cause you trouble being a rookie.. use == by default..

if(choice1 == choice2)  //condition 1
    return "The result is a tie!";
else if(choice1 == "rock") //condition 2
    if(choice2 == "scissors") 
        return "rock wins";
     else 
        return "paper wins";
else if(choice1 == "paper"){ //condition 3
    if(choice2 == "rock") 
        return "paper wins";
     else 
        return "scissors wins";
}
else if(choice1 == "scissors")
    if(choice2 == "rock")
       return "rock wins";
    else 
       return "scissors wins";

var userChoice = prompt("Do you choose rock, paper or scissors? ");


var computerChoice=Math.random();

{


if(computerChoice <= ".33") 

{
    computerChoice === 'rock';


    }


    else if(computerChoice<='.66' & '>=.34')


    {

computerChoice === 'paper';


        }

        else

{

            computerChoice ===' scissors';


            }


            }


console.log( computerChoice);

var compare = function (choice1, choice2)
{
    if (choice1 === choice2)
    {
        return "The result is a tie!";
    }
    else
    {
        if(choice1 === "rock")
        {
            if(choice2 === "paper")
            {
               return "Paper beats rock. Computer Wins.";
            }
            else
            {
                return "Rock beats scissors. You win.";

            }
        }
        else
        {
            if(choice1 === "paper")
                {
                     if(choice2 === "rock")
                        {
                             return "Paper beats rock. You Win.";
                        }
            else
                {
                return "Scissors beat paper. Computer Wins.";               }

                }
    if(choice1 === "scissors")
                {
                     if(choice2 === "rock")
                        {
                             return "Rock beats scissors. Computer Wins.";
                        }
            else
                {
                return "Scissors beat paper. You Win.";               }

                }
        }
    }



};
var r = function(user)
{
    while(user < 0 | user >3)
    {user = prompt("Please don't act oversmart. Press '1' for rock, '2' for paper, and '3' for scissors.");
    }

    if(user === "1")
    user = "rock";

    else
    {
        if(user === "2")
        {user = "paper";}
        else
        {user = "scissors";}
    };
    console.log("You chose: " + user);

    computerChoice = Math.random()
    if(computerChoice <= 0.33)
    {
        computerChoice = "rock";
    }
    else
    {
        if(computerChoice > 0.33 && computerChoice <=0.66)
        {computerChoice = "paper";}
        else
        {computerChoice = "scissors";}
    }

    console.log("The computer chose: "+computerChoice)
    console.log(compare(user, computerChoice));
    if(user===computerChoice)
    {
        userChoice = user;
        return "1";}

};


var userChoice = prompt("Press '1' for rock, '2' for paper, and '3' for scissors")
var computerChoice;

var a = r(userChoice);
if(a === "1")
{//console.log("1");
while(userChoice === computerChoice)
{
    var a = prompt("Since there was a tie, please choose again. Press 1 for rock, 2 for paper and 3 for scissors.")
    var b = r(a);
    if(b !== "1")
    {break;}
}
}

This one will create the perfect, self repeating game until someone has won. It also shows you how many games you played. All without using loops!

count = 1;

var Decisions = function() {
    if (count === 1) {
        userChoice = prompt("Do you choose rock, paper or scissors?");
    } else {
        userChoice = prompt("It's a tie. Please make your choice again!");
    }
    computerChoice = Math.random();

    if (computerChoice < 0.4) {
        computerChoice = "rock";
    } else if(computerChoice <= 0.8) {
        computerChoice = "paper";
    } else {
        computerChoice = "scissors";
    }
    console.log("User: " + userChoice);
    console.log("Computer: " + computerChoice);
}

Decisions();

var compare = function(choice1, choice2) {
    if (choice1 === choice2) {

        count = count + 1
        console.log("The result is a tie!");
        Decisions();
        return compare(userChoice, computerChoice);

    } else if (choice1 === "rock") {
        if (choice2 === "scissors") {
            return "rock wins";
        } else {
            return "paper wins";
        }
    } else if (choice1 === "paper") {
        if (choice2 === "rock") {
            return "paper wins";
        } else {
            return "scissors wins";
        }
    } else if (choice1 === "scissors") {
        if (choice2 === "paper") {
            return "scissors win";
        } else {
            return "rock wins";
        }
    }
}

console.log(compare(userChoice,computerChoice));
console.log("Wow, you played " + count + " times!");

This is the code I made at this exercise and it worked like a charm... I used logical operators on my "if" statements, and it was accepted(obviously).

Give it a try :D

var userChoice = prompt("Do you choose rock, paper or scissor?");
var computerChoice = Math.random();
if (computerChoice > 0 && computerChoice < 0.33) {
  computerChoice = "Rock";
} else if (computerChoice > 0.34 && computerChoice < 0.67) {
  computerChoice = "Paper";
} else {
  computerChoice = "Scissor";
}
console.log(computerChoice);

The solution I came to as a fellow novice seems relatively simple..

var userChoice = prompt ("Do you choose rock, paper or scissors?");

var computerChoice = Math.random();
console.log(computerChoice);

if (computerChoice <=0.33) {
    "rock";
} else if (computerChoice <=0.66) {
    "paper";
} else {
    "scissors";
}