odin-rps/index.js

const choices = ["rock", "paper", "scissors"];

function getComputerChoice() {
    return choices[Math.floor(Math.random() * 3)];
}

function playRound(playerChoice, computerChoice) {
    let playerChoiceCapital = playerChoice.slice(0,1).toUpperCase() + playerChoice.slice(1,playerChoice.length)
    let computerChoiceCapital = computerChoice.slice(0,1).toUpperCase() + computerChoice.slice(1,computerChoice.length)

    if (playerChoice == computerChoice) {
        return `It's a tie! ${playerChoiceCapital} vs ${computerChoiceCapital}.`;
    } else if ((playerChoice == "rock" && computerChoice == "paper")
            || (playerChoice == "paper" && computerChoice == "scissors")
            || (playerChoice == "scissors" && computerChoice == "rock")) {
        return `You lost! ${computerChoiceCapital} beats ${playerChoiceCapital}.`;
    } else if ((playerChoice == "rock" && computerChoice == "scissors")
            || (playerChoice == "paper" && computerChoice == "rock")
            || (playerChoice == "scissors" && computerChoice == "paper")) {
        return `You won! ${playerChoiceCapital} beats ${computerChoiceCapital}.`;
    }
}


let correctOption = false
let playerChoice;

while (correctOption == false) {
    playerChoice = prompt("What do you choose, 'rock', 'paper' or 'scissors'?").toLowerCase().trim();

    choices.forEach(element => {
        if (playerChoice == element) {
            correctOption = true
            return;
        }
    })
}

console.log(playRound(playerChoice, getComputerChoice()));