<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>检查复选框是否被选</title>
<meta charset="utf-8" />
<script src="Scripts/jquery-1.12.4.js"></script>
</head>
<body>
<form>
<input type="checkbox" id="cr" name="cr" />
<input type="checkbox" id="cr2" name="cr2" checked="checked" />
</form>
<script>
var $cr = $("#cr");//jquery对象
var cr = $cr[0]; //dom对象
var $cr2 = $("#cr2");
var cr2 = $cr2[0];
alert($cr.checked); //undefined
alert(cr.checked);//false
alert(cr2.checked);//true
</script>
</body>
</html>