return false失效，form表单直接提交了

Question

function checkUser() {
var _username = document.getElementById("j_username").value;
var _password = document.getElementById("j_password").value;
var _valcode = document.getElementById("j_valcode").value;
if (_username == "") {
alert("用户名不能为空!");
document.getElementById("j_username").focus();
return false;
}
if (_password == "") {
alert("密码不能为空!");
document.getElementById("j_password").focus();
return false;
}
if (_valcode == "") {
alert("验证码不能为空!");
document.getElementById("j_valcode").focus();
return false;
}
return true;
}

Answer 1

 <form name="testform"  action="hello.html"  method="post" onSubmit="return check();">