Solve - Cannot set property 'onchange' of Null in JS

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Borislav Hadzhiev

Tue Oct 19 20212 min read

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Solve - Cannot set property 'onchange' of Null #

The "Cannot set property 'onchange' of null" error occurs for 2 reasons:

  1. Setting the onchange 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.

cannot set property onchange of null

Here's an example of how the error occurs.

index.js
const input = null; // ⛔️ Cannot set properties of null (setting onchange) input.onchange = function handleChange(event) { console.log(event.target.value); };

To solve the "Cannot set property 'onchange' of null" error, make sure the id you're using to access the element exists in the DOM. The error often occurs after providing a non-existent id to the getElementById method.

index.js
const input = document.getElementById('does-not-exist'); console.log(input); // 👉️ null // ⛔️ Cannot set properties of null (setting onchange) input.onchange = function handleChange(event) { console.log(event.target.value); };

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

Setting the onchange property on a null value causes the error.

To solve the "Cannot set property 'onchange' 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> <!-- ⛔️ BAD - script runs before input exists ⛔️ --> <script src="index.js"></script> <input id="first_name" name="first_name" type="text" /> </body> </html>

We placed the JS script tag above the code that creates the input element. This means that the index.js file is ran before the input is created, therefore we don't have access to the input element in the index.js file.

index.js
const input = document.getElementById('first_name'); console.log(input); // 👉️ null // ⛔️ Cannot set properties of null (setting onchange) input.onchange = function handleChange(event) { console.log(event.target.value); };

The JS script tag should be moved to the bottom of the body, after all of the DOM elements it needs access to.

index.html
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8" /> </head> <body> <input id="first_name" name="first_name" type="text" /> <!-- ✅ GOOD - input already exists ✅ --> <script src="index.js"></script> </body> </html>

Now, the index.js file has access to the input element.

index.js
const input = document.getElementById('first_name'); console.log(input); // 👉️ input#first_name // ✅ Works input.onchange = function handleChange(event) { console.log(event.target.value); };

Conclusion #

The "Cannot set property 'onchange' of null" error occurs when trying to set the onchange property on a null value.

To solve the error, run the JS script after the DOM elements are available and make sure you only set the property on valid DOM elements.

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