Untitled

<!DOCTYPE html>

<html>
	<head>
		<style>
		.odd {
			background-color: blue;
		}

		.even {
			background-color: yellow;
		}

		</style>

	</head>

	<body>

		<ul id="listing">

		</ul>

		<button type="button" onclick="addElement()">Add element</button>
		<button type="button" onclick="removeElement()">Remove element</button>

	<script>

	//create a variable = 0  so
	var i = 0;

		function addElement(){
			var x = document.createElement("LI");

			// check if i is divisible by 2
			if(i % 2 == 0){
				// if it is, set the class to odd
				x.setAttribute("class", "odd");
			}else{
				// else set it to even
				x.setAttribute("class", "even");
			}
			x.innerHTML = "some text";
			document.getElementById("listing").appendChild(x);
			// add 1 to i
			i++;
		}

		function removeElement(){
			var y = document.getElementById("listing");
			y.removeChild(y.lastChild);
		}

	</script>

	</body>

</html>