Form Validation Before Sending To PHP Script?

I'm having trouble validating a form with javascript before sending it to a php script. Even when the form fails validation it still sends to the php. I believe it's to do with my validation script. You can see the script live here: [URL]

HTML Form:
Code HTML4Strict:
<form action="includes/verify_login.php" onsubmit="return validate_login(this);" method="post" name="login_form">
<label for="user">Username</label><input type="text" class="custom_field" name="user" id="user">
<label for="pass">Password</label><input type="password" class="custom_field" name="pass" id="pass">
<input type="checkbox" id="remember" name="remember"><label id="label_remember" for="remember">Remember Me</label><br>
<button id="custom_button">Login</button>
</form>

Javascript:
Code JavaScript:
function validate_required(field){
with(field){
if (value==null||value==""){
document.getElementById("empty").style.display="block";
return false;
}else{
return true;
}}}
 
function validate_login(thisform){
with (thisform){
if (validate_required(user)==false){
name.focus();
return false;
}else if (validate_required(pass)==false){
comment.focus();
return false;
}else{
return true;
}}}