jQuery函数继承 $.extend, $.fn.extend

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Test jQuery Extend</title>
    <script src="jquery-1.12.4.min.js"></script>
    <script>
        (function($){
            /*类插件 usage: $.add(1,2) */
            $.extend({
                add: function(a,b){return a+b;},
                minus: function(a,b){return a-b;}
            });
            /*实例插件 usage: $("#name").strlen() */
            $.fn.extend({
                strlen: function () {
                    return $(this).text().length;
                }
            });
        })(jQuery);

        $(function () {
            console.log($.add(1,2));
            console.log($.minus(1,2));
            console.log('字符长度',$("#name").strlen());
        });
    </script>
</head>
<body>
    <div id="name">abcd123中国</div>
</body>
</html>