手动编写JQUERY插件

<script type="text/javascript">
    //编写插件
    (function ($) {
        $.fn.placeholder = function (option) {
            var input = this;
            input.focus(function () {
                if (input.val() == "" || input.val() == option.DefaultValue) {
                    input.val("");
                    if (option.WritingColor == undefined) option.WritingColor = "#000000";
                    input.css("color", option.WritingColor);
                }
            });
            input.blur(function () {
                if (input.val() == "") {
                    input.val(option.DefaultValue);
                    if (option.DefaultColor == undefined) option.DefaultColor = "#000000";
                    input.css("color", option.DefaultColor);
                }
            });
            if (input.val() == "") input.blur();
        }
    })(jQuery);
    //调用
    $("#username").placeholder({ DefaultValue: "请输入用户名",DefaultColor:"#888",WritingColor:"#000000" });
    </script>