Example with insert and remove elements

Playing around with this

by Megi93

HTML

<button>Add fries to lunch</button>
<button>Add Jogurt to lunch</button>
<button>Add cheese to sandwich</button>
<button>Add ketchup to sandwich</button>
<button>Remove pickles</button>
<button>Remove mayo</button>
<h3>My Lunch</h3>
<ul id="lunch">
    <li>
        <h4>My sandwich</h4>
    </li>
    <li>Bread</li>
    <li id="pickles">Pickles</li>
    <li id="Beef">Beef</li>
    <li id="Mayo">Mayo</li>
    <li id="bread">Bread</li>
</ul>

JavaScript

var lunch = document.querySelector("#lunch");
var btn = document.querySelectorAll("button");

var addFries = function() {
    var fries = document.createElement("div");
    fries.innerHTML = '<li><h4>Fries</h4></li>';
    //adding to lunch fries
    lunch.appendChild(fries);
}

var addJoghurt = function() {
    var joghurt = document.createElement("li");
    joghurt.innerHTML = '<li><h4>Joghurt</h4></li>';
    lunch.appendChild(joghurt);
}

var addCheese = function() {
    var beef = document.querySelector("#Beef");
    var topSlice = document.createElement("li");
    var bottomSlice = document.createElement("li");

    //adding to topSlice and bottomSlice text inside
    topSlice.innerHTML = bottomSlice.innerHTML = 'Cheese';
    beef.parentNode.insertBefore(topSlice, beef);
    beef.parentNode.insertBefore(bottomSlice, beef.nextSibling);
}

var addKetchup = function() {
    var bread = document.querySelector("#bread");
    var topSlice = document.createElement("li");
    topSlice.innerHTML = 'Ketchup';
    bread.parentNode.insertBefore(topSlice, bread);
}

var removePickles = function() {
    var pickle = document.querySelector("#pickles");
    if (pickle) {
        pickle.parentNode.removeChild(pickle);
    }
}

var removeMayo = function() {
    var mayo = document.querySelector("#Mayo");
    if (mayo) {
        mayo.parentNode.removeChild(mayo);
    }
}

btn[0].addEventListener("click", addFries);
btn[1].addEventListener("click", addJoghurt);
btn[2].addEventListener("click", addCheese);
btn[3].addEventListener("click", addKetchup);
btn[4].addEventListener("click", removePickles);
btn[5].addEventListener("click", removeMayo);