框架下载地址：http://modernizr.com/
案例：
<!DOCTYPE html>
<html>
<head>
<script src="http://code.jquery.com/jquery-1.7.1.js"></script>
<script src="http://ajax.cdnjs.com/ajax/libs/modernizr/1.7/modernizr-1.7.min.js">
</script>
<script type="text/javascript">
$(function(){
if( !Modernizr.input.required ){
var $msg = $( "<div id='reqMessage'>Required Fields Missing</div>" );
$msg.css( "background-color", "yellow" )
.hide();
$( "body" ).append( $msg );
$( "#fDet" ).on( "submit", function(e){
$( "input[required]" ).each(function(){
if ( $( this ).val() === "" ) {
$( "#reqMessage" ).show();
$( this ).css( "border" , "1px solid red" );
e.preventDefault();
}
});
});
}
});
</script>
</head>
<body>
<form id="fDet" action="#">
<input type="text" name="userName" required/>
<input type="password" name="password" required/>
<input type="submit" value="send it" />
</form>
</body>
</html>
