Borislav Hadzhiev
Last updated: Oct 21, 2021
Check out my new book
The "Cannot read property 'offsetHeight' of null" error occurs for 2 reasons:
offsetHeight
property on a null
value (DOM element that
doesn't exist).Here is an example of how the error occurs.
const el = null; // ⛔️ Cannot read properties of null (reading 'offsetHeight') console.log(el.offsetHeight);
To solve the "Cannot read property 'offsetHeight' of null" error, make sure
the id
you're using to get the element is present in the DOM. The error often
occurs after providing a non-existent id
to the getElementById
method.
const el = document.getElementById('does-not-exist'); console.log(el); // 👉️ null // ⛔️ Cannot read properties of null (reading 'offsetHeight') console.log(el.offsetHeight);
We passed a non-existent id
to the getElementById()
method and got a null
value back.
Accessing the offsetHeight
property on a null
value causes the error.
To solve the "Cannot read property 'offsetHeight' of null" error, place the JS script tag at the bottom of the body tag. The script should run after the DOM elements have been created.
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8" /> </head> <body> <!-- ❌ BAD - script runs before div exists ❌ --> <script src="index.js"></script> <div id="box">Test</div> </body> </html>
The JS script tag is placed above the code that creates the div
element,
therefore the element won't be accessible in the index.js
file.
const el = document.getElementById('box'); console.log(el); // 👉️ null // ⛔️ Cannot read properties of null (reading 'offsetHeight') console.log(el.offsetHeight);
Instead, we should place the JS script tag at the bottom of the body tag, after the elements we need to access.
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8" /> </head> <body> <div id="box">Test</div> <!-- ✅ GOOD - div already exists ✅ --> <script src="index.js"></script> </body> </html>
Now we can access the div
inside of the index.js
file.
const el = document.getElementById('box'); console.log(el); // 👉️ div#box // ✅ Works console.log(el.offsetHeight); // 👉️ 18
The "Cannot read property 'offsetHeight' of null" error occurs when trying to
access the offsetHeight
property on a null
value.
To solve the error, run the JS script after the DOM elements are available and make sure you only access the property on valid DOM elements.