How to fix the "document is not defined" error in SvelteKit

One of the most common errors you will encounter while using SvelteKit is the `document is not defined ` error. This can be caused when you either try to access the `document` object inside a `script` tag or import a function that uses the `document` object. In this article, we will look at why this error occurs and how to fix it.

Why does the "document is not defined" error occur?

By default, SvelteKit will render your components on the server. The components will be rendered in the browser using hydration on subsequent requests. That means that at some point in the component lifecycle, particular browser-specific objects like  document document  will not be available .

So in this example, we are trying to access the  document  object inside a  script  tag:

When we run this code, we get an internal server error displayed in the browser. And the following in the Node.js console:

How to fix the "document is not defined" error

You can use a few ways to fix this error, depending on the situation.

Use SvelteKit  browser  module

SvelteKit provides a built-in module called  browser  that you can use to check the environment your code is running in, whether it's the browser or the server. Here is how you can use it to fix the "document is not defined" error:

Here we are only executing the code that uses the  document  object if we are in the browser.

Use the  onMount  lifecycle function

Another way to fix the "document is not defined" error is to use the  onMount  lifecycle function from  svelte . This function is called when the component is to the DOM. So you can use it to run code that uses the  document  object.

Conclusion

That's it. I hope this article was helpful!