// 1. Create the button
var button = document.createElement("button");
button.innerHTML = "Do Something";
// 2. Append somewhere
var body = document.getElementsByTagName("body")[0];
body.appendChild(button);
// 3. Add event handler
button.addEventListener ("click", function() {
alert("did something");
});
/* Read
https://css-tricks.com/use-button-element/
*/