Inspect the checked property of the element.

Say you have this checkbox:

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

You can see if it’s checked using

document.querySelector('.checkbox').checked

You can also check if looking for .checkbox:checked does not return null:

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

but I think looking for .checked is cleaner.

Do NOT use getAttribute() looking for the checked attribute value, because that’s always true if the checkbox is checked by default in this way:

<input type="checkbox" checked />

Also don’t check for the value of a checkbox element. It’s always on, regardless whether the checkbox is checked or not.

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