<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<title></title>
<link rel="stylesheet" href="">
<script>
$( "#container" ).on( "click", "input", function( event ) {
var input = e.target;
var arr = [];
if
( input.is(':checked')=='1')
{
arr.push(input.val);
console.log(input.length);
} else {
arr.shift(input.val);
console.log(input.length);
}
});
</script>
</head>
<body>
<div id="container">
<p><label><input type="checkbox" id="chk1" value="1" />1</label></p>
<p><label><input type="checkbox" id="chk2" value="3" />2</label></p>
<p><label><input type="checkbox" id="chk3" value="5" />3</label></p>
<p><label><input type="checkbox" id="chk4" value="7"/>4</label></p>
</div>
</body>
</html>