Print 'Hello World'

<button onclick="showHelloWorld()">Show "Hello World"</button> 

<button onclick="eraseHelloWorld()">Erase "Hello World"</button>

<p id="demoHelloWorld"></p>

<script>

    function showHelloWorld() {

        document.getElementById("demoHelloWorld").innerHTML = "Hello World";}

   function eraseHelloWorld() {

        document.getElementById("demoHelloWorld").innerHTML = "";}

</script>