Borislav Hadzhiev
Sat Oct 23 2021·2 min read
Photo by Felipe Elioenay
There are 2 reasons the "Cannot read property 'classList' of null" error occurs:
classList
property on a null
value - a DOM element that
doesn't exist.Here is an example of how the error occurs.
const box = document.getElementById('does-not-exist'); console.log(box); // 👉️ null // ⛔️ Cannot read properties of null (reading 'classList') box.classList.add('bg-green-400');
To solve the "Cannot read property 'classList' of null" error, make sure the
id you're using to get the DOM element is valid and exists in the DOM. The error
often occurs when providing an invalid id
to the getElementById
method.
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8" /> </head> <body> <!-- 👇️ id should match with JS code --> <div id="box">Hello</div> <script src="index.js"></script> </body> </html>
To solve the "Cannot read property 'classList' of null" error, place the JS script tag at the bottom of the body tag. The JS script tag should be ran after the HTML elements are declared.
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8" /> </head> <body> <!-- ⛔️ BAD - script runs before div is created ⛔️ --> <script src="index.js"></script> <div id="box">Hello</div> </body> </html>
The index.js
script is ran before the HTML elements have been created,
therefore you can't access the HTML elements in the index.js
file.
const box = document.getElementById('box'); console.log(box); // 👉️ null // ⛔️ Cannot read properties of null (reading 'classList') box.classList.add('bg-green-400');
Instead, you should place the script tag after the DOM elements have been declared.
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8" /> </head> <body> <div id="box">Hello</div> <!-- ✅ GOOD - div already exists ✅️ --> <script src="index.js"></script> </body> </html>
Now the div
with id
of box
is accessible inside the index.js
file.
const box = document.getElementById('box'); console.log(box); // 👉️ div#box // ✅ works box.classList.add('bg-green-400');
The "Cannot read property 'classList' of null" error occurs when trying to
access the classList
property on a null
value.
To solve the error, make sure the JS script tag is loaded after the HTML is
created and the id
of the element exists in the DOM.