app.js

let gameSeq= [];
let userSeq= [];

let btns = ["yellow", "red" , "purple" , "green"];

let started = false;
let level = 0;

let h2 = document.querySelector("h2");

document.addEventListener("keypress", function() {
    if(started == false) {
        console.log("game is started");
        started = true;

        levelUp();
    }
});

function gameFlash(btn) {
    btn.classList.add("flash");
    setTimeout(function () {
        btn.classList.remove("flash");
    }, 250);
}

function userFlash(btn) {
    btn.classList.add("userflash");
    setTimeout(function () {
        btn.classList.remove("userflash");
    }, 250);
}

function levelUp() {
    userSeq = [];
    level++
    h2.innerText = `Level ${level}`;
    
    let randIdx = Math.floor(Math.random() * 4);
    let randColor = btns[randIdx];
    let randBtn = document.querySelector(`.${randColor}`);
    gameSeq.push(randColor);
    console.log(gameSeq);
    gameFlash(randBtn);
}

function checkAns(idx) {
    if(userSeq[idx] === gameSeq[idx]) {
        if(userSeq.length == gameSeq.length) {
            setTimeout(levelUp,1000);
        }
    } else {
        h2.innerHTML = `Game Over!Your score was <b>${level}</b> <br> Press any key to start`;
        document.querySelector("body").style.backgroundColor = "red";
        setTimeout(function () {
            document.querySelector("body").style.backgroundColor = "white";
        }, 150);
        reset();
    }
}

function btnPress() {
    let btn = this;
    userFlash(btn);

    userColor = btn.getAttribute("id");
    userSeq.push(userColor);

    checkAns(userSeq.length -1);
}

let allBtns = document.querySelectorAll(".btn");
for (btn of allBtns) {
    btn.addEventListener("click", btnPress);
}

function reset() {
    started = false;
    gameSeq = [];
    userSeq = [];
    level = 0;
}