Simple click event JS
HTML
<p id="button">Click</p>
<p id="demo"></p>
CSS
body {font-family: Arial;}
#button {cursor: pointer;}
JavaScript
var hello;
var greeting = "Hi"
hello = (val) => greeting + " " + val;
document.querySelector("#button").addEventListener("click", function() {
document.querySelector("#demo").innerHTML = hello("there!");
});