let username = document.getElementById("username");
    let pwd_1 = document.getElementById("password");
    let pwd_2 = document.getElementById("password-2");

    const reUsername = /^[0-9A-Za-z]{3,10}$/;
    const rePwd = /^[0-9A-Za-z]{6,20}$/;

    if(!reUsername.exec(username.value) || !rePwd.exec(pwd_1.value) || pwd_1.value !== pwd_2.value){
        alert("please recheck your password or username!")
        return false;
    }