<html>
<head>
<script src="https://libs.baidu.com/jquery/1.10.2/jquery.min.js">
</script>
<script>
$(document).ready(function(){
$("input").focus();
$(":focus").css("background-color","yellow");
});
</script>
</head>
<body>
<input type="text">
</body>
</html>