JSFiddle - React, Tailwind, and code Playground

JavaScript

var user;
var compare = function (computer, user) {
    if (computer === "rock") {
        if (user === "scissors") {
            return "Computer wins by choosing rock!";
        }
    } else if (computer === "scissors") {
        if (user === "paper") {
            return "Computer wins by choosing scissors!";
        }
    } else if (computer === "paper") {
        if (user === "rock") {
            return "Computer wins by choosing paper!"
        }
    }

    if (computer === user) {
        return ("It is a tie!")
    } else if (user === "paper") {
        if (computer === "rock") {
            return ("You win by choosing paper!")
        }
    } else if (user === "rock") {
        if (computer === "scissors") {
            return ("You win by choosing scissors!")
        }
    } else if (user === "scissors") {
        if (computer === "paper") {
            return ("You win by choosing scissors!")
        }
    }
};

while (user != "rock" && user != "paper" && user != "scissors") {
    user = prompt("Do you choose rock, paper or scissors?")
    if (user == null) {
        break;
    }
};

if (user != null) {
    var computer = Math.random();
    if (computer < 0.34) {
        computer = "rock";
    } else if (computer <= 0.67) {
        computer = "paper";
    } else {
        computer = "scissors";
    }

    console.log("Computer Chooses: " + computer);
    console.log("User Chooses: " + user);
    console.log(compare(computer, user));
}