SimonGame.js

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

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

let started = false;
let level = 0;

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

document.addEventListener("click",function(){
    if(started == false){
        console.log("Game Started");
        started = true;

        levelUp();
    }
});

document.addEventListener("keypress",function(){
    if(started == false){
        console.log("Game 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()*3);
    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';
        },500)
        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;
}