rock-paper-scissors.js

// Standalone, dependency-free version of rock paper scissors
// Author: Marc Backes (@themarcba)

// Available choices and it's associated values
const choiceMap = { r: 'rock', p: 'paper', s: 'scissors' }

// Request an input from the user
const getInput = query => {
    return new Promise((resolve, reject) => {
        const readline = require('readline').createInterface({
            input: process.stdin,
            output: process.stdout,
        })
        readline.question(`${query} `, choice => {
            readline.close()
            resolve(choice.toLowerCase())
        })
    })
}

// Make the computer pick a move
const aiMove = () => {
    const possibilities = Object.values(choiceMap)
    const randomIndex = Math.floor(Math.random() * possibilities.length)
    return possibilities[randomIndex]
}

// Make the player pick a move
const playerMove = async () => {
    return new Promise(async (resolve, reject) => {
        let input = ''
        // Avoid wrong inputs
        while (!(input in choiceMap)) {
            input = await getInput('Rock, Paper, Scissors? (R/P/S)')
            if (!(input in choiceMap)) console.log(`Invalid choice. Try again.`)
            else resolve(choiceMap[input])
        }
    })
}

// Tell whether the player won or lost
const evaluate = (ai, player) => {
    if (ai === player) return 'draw'
    if (player === 'rock' && ai === 'scissors') return 'win'
    if (player === 'paper' && ai === 'rock') return 'win'
    if (player === 'scissors' && ai === 'paper') return 'win'
    return 'lose'
}

// Run the game in an endless loop
const run = async () => {
    const score = { ai: 0, player: 0 }
    while (true) {
        console.log('-----------------------------------')

        // Gather inputs and evaluate
        const ai = aiMove()
        const player = await playerMove()
        const result = evaluate(ai, player)

        // Output results
        console.log(`You played ${player}`)
        console.log(`The AI played ${ai}`)
        console.log(result)
        if (result === 'draw') {
            console.log(`It's a draw!`)
        } else if (result === 'win') {
            console.log(`You won!`)
            score.player++
        } else if (result === 'lose') {
            console.log(`You lost!`)
            score.ai++
        }
        console.log('Current scores:', { score })
    }
}

run()

To run this, just feed it to Node.js. No further steps are required.

node rock-paper-scissors.js

Half of this code you see here was written by GitHub Copilot 🤖