Use the checked property of the checkbox element. Example:

<input type="checkbox" class="checkbox" />

To check whether it is checked:

document.querySelector('.checkbox').checked

Alternatively, check whether a checked checkbox exists:

document.querySelector('.checkbox:checked') !== null

Using the .checked property is usually clearer.

Do not use getAttribute('checked') to determine checked state; the attribute does not reflect user toggles. For example:

<input type="checkbox" checked />

Do not rely on the checkbox’s value for checked state—it is always on when present.

Lessons in this unit:

0:	Introduction
1:	The File object
2:	FileList
3:	FileReader
4:	Blob
5:	FormData
6:	Accept only images in file input
7:	▶︎ Check if checkbox is checked
8:	Reset a form
9:	File upload with server handling
10:	Drag and drop file upload
11:	Validating file size before upload