var styleListElements = function(){
  var list_items = document.querySelectorAll("div#essentials > ul > li");
  for (var i = list_items.length - 1; i >= 0; i--) {
    // for (initializer, condition, counter)
    list_items[i].style.backgroundColor = "yellow";
    list_items[i].addEventListener("click", selectItem);
  }
};

var selectItem = function(event){
  // console.log(this.innerHTML);
  this.classList.add("selected");
  document.querySelector("img").setAttribute("src","./images/" + this.innerHTML + ".jpeg");
};

var changeGreeting = function(){
  var greeting_div = document.getElementById("greeting");
  greeting_div.innerHTML = "Hello Planet earth!";
};

var resetButtonHandler = function() {
  var list_items = document.querySelectorAll("li");
  for (var i = list_items.length - 1; i >= 0; i--) {
    list_items[i].className = "";
  }
  document.querySelector("img").setAttribute("src","./images/panic.jpeg");
};

var initialize = function(){
  changeGreeting();
  styleListElements();
  document.querySelector("#reset").addEventListener("click",resetButtonHandler);
};

window.onload=initialize;