add dom elements w3schools code example
Example 1: insert element to dom
var node = document.createElement("LI"); // Create a <li> node
var textnode = document.createTextNode("Water"); // Create a text node
node.appendChild(textnode); // Append the text to <li>
document.getElementById("myList").appendChild(node); // Append <li> to <ul> with id="myList"
Example 2: how to add elements in javascript html
//adding 'p' tag to body
var tag = document.createElement("p"); // <p></p>
var text = document.createTextNode("TEST TEXT");
tag.appendChild(text); // <p>TEST TEXT</p>
var element = document.getElementsByTagName("body")[0];
element.appendChild(tag); // <body> <p>TEST TEXT</p> </body>