var username = document.getElementById('username');

var pwd = document.getElementById('password');

var pwd2 = document.getElementById('password-2');

var regExp1 = /[0-9a-zA-Z]{3,10}/;

var regExp2 = /[\S]{6,20}/;

if(!regExp1.test(username.value)){

    window.alert('用户名输入错');

    return false;

}

if(!regExp2.test(pwd.value)){

    window.alert('密码不合要求');

    return false;

}

if(pwd.value !== pwd2.value){

    window.alert('密码输入不一致');

    return false;

}

    return true;