game.js

var buttonColours = ["red", "blue", "green", "yellow"];

var gamePattern = [];

var userClickedPattern = [];

var started = false;

var level = 0;

$(document).keypress(function() {
    if (!started) {
        $("#level-title").text("Level " + level);
        nextSequence();
        started = true;
    }
});

$(".btn").on("click", function() {
    var userChosenColour = $(this).attr("id");

    userClickedPattern.push(userChosenColour);

    playSound(userChosenColour);

    animatePress(userChosenColour);

    checkAnswer(userClickedPattern.length-1);
});

function nextSequence() {
    userClickedPattern = [];

    level++;

    $("#level-title").text("Level " + level);

    var randomNumber = Math.floor(Math.random() * 4);

    var randomChosenColour = buttonColours[randomNumber];

    gamePattern.push(randomChosenColour);

    $("#" + randomChosenColour).fadeOut(100).fadeIn(100).fadeOut(100).fadeIn(100);

    playSound(randomChosenColour);
}

function playSound(name) {
    var audio = new Audio("sounds/" + name + ".mp3");

    audio.play();
}

function animatePress(currentColour) {
    $("#" + currentColour).addClass("pressed");
    setTimeout(function () {
        $("#" + currentColour).removeClass("pressed");
    }, 100);   
}

function checkAnswer(currentLevel) {
    if(gamePattern[currentLevel] === userClickedPattern[currentLevel] ) {
        if (userClickedPattern.length === gamePattern.length) {
            setTimeout(function () {
              nextSequence();
            }, 1000);   
        } 
    } else {
        playSound("wrong");

        $("body").addClass("game-over");
        setTimeout(function() {
            $("body").removeClass("game-over");
        }, 200);

        $("#level-title").text("Game Over, Press Any Key to Restart");

        startOver();
    }
}

function startOver() {
    level = 0;
    gamePattern = [];
    started = false;
}