What is the DOM?

The DOM (Document Object Model) is the browser's live, tree-shaped model of your HTML page. Every tag becomes an object that JavaScript can read and change.

<body>
  <h1>Hello</h1>
  <ul>
    <li>One</li>
    <li>Two</li>
  </ul>
</body>

In the DOM, <body> is the parent of <h1> and <ul>, and <ul> is the parent of the two <li> elements. Change the DOM and the page on screen updates immediately.