sign up form with flex and js dom

I find it difficult on working with the js dom it takes a time to find a solution from the internet but I manage to solve it. but there's a flaw with my project, it supposes to clear all the input in the form but when I try to put a date on one text input and leave all other input empty the form will have this class error but the input that I entered has been cleared which is wrong considering I have no text entered on other input.