javascript - Why does jQuery or a DOM method such as getElementById not find the element?

Question

What are the possible reasons for document.getElementById, $("#id") or any other DOM method / jQuery selector not finding the elements?

Example problems include:

• jQuery silently failing to bind an event handler
• jQuery "getter" methods (.val(), .html(), .text()) returning undefined
• A standard DOM method returning null resulting in any of several errors:

Uncaught TypeError: Cannot set property '...' of null
Uncaught TypeError: Cannot set properties of null (setting '...')
Uncaught TypeError: Cannot read property '...' of null
Uncaught TypeError: Cannot read properties of null (reading '...')

The most common forms are:

Uncaught TypeError: Cannot set property 'onclick' of null
Uncaught TypeError: Cannot read property 'addEventListener' of null
Uncaught TypeError: Cannot read property 'style' of null

Answer 1

The element you were trying to find wasn’t in the DOM when your script ran.

The position of your DOM-reliant script can have a profound effect upon its behavior. Browsers parse HTML documents from top to bottom. Elements are added to the DOM and scripts are (generally) executed as they're encountered. This means that order matters. Typically, scripts can't find elements which appear later in the markup because those elements have yet to be added to the DOM.

Consider the following markup; script #1 fails to find the <div> while script #2 succeeds:

<script>
  console.log("script #1:", document.getElementById("test")); // null
</script>
<div id="test">test div</div>
<script>
  console.log("script #2:", document.getElementById("test")); // <div id="test" ...
</script>