need:
When the input box loses focus: judge, if the content of the input box is empty, get the focus; otherwise, the content of the input box will pop up.
<!DOCTYPE html>
<html>
<head>
<title>Determine whether the input is empty</title>
<script src="https://apps.bdimg.com/libs/jquery/2.1.4/jquery.min.js"></script>
</head>
<body>
输入框：<input type="text" name="shurukuang" id="inputbox">
<script type="text/javascript">
// When the input box loses focus: judge
// If the content of the input box is empty, get the focus;
// If the content of the input box is not empty, the content of the input box will pop up
$( function () {
$('#inputbox').blur(function(event) {
if ($(this).val()=='') {
$(this).focus();
}else{
alert($(this).val());
}
});
})
</script>
</body>
</html>