<html>
<head>
<meta charset=utf-8>
</head>
<body>
<form>
<label>牛客会陪伴大家</label>
<input id="checkbox" type="checkbox" checked />
</form>
</body>
<script type="text/javascript">
// 补全代码
var cb = document.querySelector('#checkbox');
cb.onclick = function(){
if (cb.checked){}else{cb.checked = true;}
}
</script>
</html>