add text to html element javascript code example

Example 1: js add more text to element

document.getElementById("p").textContent += " This is the text from javascript.";

<p id ="p">This is the text from HTML.</p>

Example 2: how to add text in javascript

<div id="mass">
<p id="ph1">This is a paragraph.</p>
<p id="ph2">This is another paragraph.</p>
</div>

<script>
var head = document.createElement("h1");
var node = document.createTextNode("New Heading.");
head.appendChild(node);

var ele = document.getElementById("mass");
var child = document.getElementById("ph1");
ele.insertBefore(head,child);
//ele.append(head,child);

Output : 
New Heading.
This is a paragraph.
This is another paragraph.