JavaScript: getElementById

getElementById() finds the element whose id matches a string, so a script can read or update that element.

What you will learn

How an HTML id connects to JavaScript
How to update text with textContent
Why a missing element returns null

Minimal example

<p id="message">Waiting...</p>
<script>
  const message = document.getElementById('message');
  if (message) message.textContent = 'Ready';
</script>

The id should be unique in the document. Use textContent for plain text so a value is not interpreted as HTML.

Common mistakes

Call the code after the element exists, such as after the script at the end of the body or DOMContentLoaded.
Check for null when the element may not be present.
Do not reuse an id for several elements; use a class or a selector when you need a collection.