Rock, Paper and Scissors Game using JavaScript

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