Why do the '.lenght' doesn't work ?

Question

https://code.sololearn.com/WjnV1qnET52c/?ref=app
I did that but when i click on the submit button it displays 'undefined'

Answer 1

FIRST ERROR:
it is "length" not "lenght"
SECOND ERROR:
when you want to compare with ' ' you should use === not ==
like that: if($('#username').val() === '') {
BTW it is nice code :D

Answer 2

Is written "length".