what is insertbefore() or appendchild() method in javascript code example

Example 1: js insertbefore

// The Node.insertBefore() method inserts a node before a
// reference node as a child of a specified parent node.
let insertedNode = parentNode.insertBefore(newNode, referenceNode)

Example 2: appendchild javascript

const parent = document.createElement('div');
const child = document.createElement('p');
const childTwo = document.createElement('p');
parent.append(child, childTwo, 'Hello world'); // Works fine
parent.appendChild(child, childTwo, 'Hello world');
// Works fine, but adds the first element and ignores the rest