onblur.html:20 Uncaught TypeError: Cannot set properties of null

This error message indicates that you are trying to set a property on a null object. In other words, you are trying to access an element in the document that does not exist.

The error is occurring on line 20 of the onblur.html file, which suggests that there is an issue with the code on that line. Without seeing the code, it is difficult to determine the exact cause of the error.

Here are a few common reasons why this error might occur:

- The element you are trying to access does not exist in the HTML document.
- The element is not yet loaded when the JavaScript code is executed.
- There is a typo in the element ID or class name, causing the code to search for a non-existent element.

To fix the error, you should check the code on line 20 and make sure you are accessing the correct element. You should also ensure that the element exists in the HTML document and is loaded before the JavaScript code is executed. Finally, double-check any IDs or class names to make sure they are spelled correctly.