Solve - Cannot read property 'offsetWidth' of Null in JS

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Borislav Hadzhiev

Thu Oct 21 20212 min read

Solve - Cannot read property 'offsetWidth' of Null #

The "Cannot read property 'offsetWidth' of null" error occurs for 2 reasons:

  1. Accessing the offsetWidth property on a null value (DOM element that doesn't exist).
  2. Placing the JS script tag above the HTML where the DOM elements are declared.
index.js
const el = null; // โ›”๏ธ Cannot read properties of null (reading 'offsetWidth') console.log(el.offsetWidth);

To solve the "Cannot read property 'offsetWidth' of null" error, make sure the id you're using to get the element is contained in the DOM. The error often occurs after providing a non-existent id to the getElementById method.

index.js
const el = document.getElementById('does-not-exist'); console.log(el); // ๐Ÿ‘‰๏ธ null // โ›”๏ธ Cannot read properties of null (reading 'offsetWidth') console.log(el.offsetWidth);

We passed a non-existent id to the getElementById method and got a null value back.

Accessing the offsetWidth property on a null value causes the error.

To solve the "Cannot read property 'offsetWidth' 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.

index.html
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8" /> </head> <body> <!-- โ›”๏ธ BAD - script runs before div exists โ›”๏ธ --> <script src="index.js"></script> <div id="box">Text 1</div> </body> </html>

Notice that the JS script tag is placed above the HTML code that declares the div element.

The index.js file is executed before the div element is created, therefore we can't access the div in the file.

index.js
const el = document.getElementById('box'); console.log(el); // ๐Ÿ‘‰๏ธ null // โ›”๏ธ Cannot read properties of null (reading 'offsetWidth') console.log(el.offsetWidth);

Instead, move the JS script tag to the bottom of the body, after the DOM elements you need to access.

index.html
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8" /> </head> <body> <div id="box">Text 1</div> <!-- โœ… GOOD - div already exists โœ… --> <script src="index.js"></script> </body> </html>

Now we can access the div element inside the index.js file.

index.js
const el = document.getElementById('box'); console.log(el); // ๐Ÿ‘‰๏ธ div#box // โœ… Works console.log(el.offsetWidth); // ๐Ÿ‘‰๏ธ 1653
The offsetWidth property rounds the value to an integer. If you need a fractional value, use the getBoundingClientRect() method.

Conclusion #

The "Cannot read property 'offsetWidth' of null" error occurs when trying to access the offsetWidth 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.

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