script.js

form=document.querySelector('form');

username=document.querySelector('#uname');
email=document.querySelector('#email');
pass=document.querySelector('#password');

unordered=document.querySelector('#error');

const re =
  /^(([^<>()[\]\.,;:\s@\"]+(\.[^<>()[\]\.,;:\s@\"]+)*)|(\".+\"))@(([^<>()[\]\.,;:\s@\"]+\.)+[^<>()[\]\.,;:\s@\"]{2,})$/i;

form.addEventListener("submit" , (e) => {
    error_list = [];
    if (username.value == ''){
        error_list.push("username is empty");
    }

    if (re.test(email.value) == false) {
        error_list.push("eamil is not valid");
    }

    if (pass.value.length <10) {
        error_list.push("password is weak! choose an other password");
    }

    if (error_list.length > 0) {
        e.preventDefault();
        error_list.forEach((element) => {
            console.log(element);
            list_item=document.createElement('li');
            list_item.innerText= element;
            unordered.appendChild(list_item);
        });
    }
 });