//jquery插件

($.fn.jason = function(a) {
    var b = {
        focus: "black",
        unfocus: "#999"
    }, c = $.extend(b, a);
    return $(this).each(function() {
        if (!$.support.leadingWhitespace||($.browser.msie && $.browser.version < 10)) {//判断ie,如果jQuery版本过高就不能使用后面的判断
            var a = $(this).attr("placeholder");
            $(this).val(a), $(this).css("color", c.unfocus), $(this).focus(function() {
                ($(this).val() == a || "" == $(this).val()) && ($(this).attr("placeholder", ""),
                $(this).val(""), $(this).css("color", c.focus));
            }), $(this).blur(function() {
                ($(this).val() == a || "" == $(this).val()) && ($(this).val(a), $(this).css("color", c.unfocus));
            });
        }
    });
})(jQuery);