validation javascript

function validate(form) {

var reg = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;

if (document.getElementById("txtName").value == "") {
alert("Please input a valid name.");
return false;
}

if(reg.test(document.getElementById("txtEmail").value) == false) {
alert("Please input a valid email.");
return false;
}

if (!document.getElementById("chkAgree").checked) {
alert("You have not agreed to the terms and conditions.");
return false;
}

return true;
}

<form method="post" action="" onsubmit="return validate(this)">