(function ($) { $.fn.watermark = function (options) {  var settings = $.extend({   watermarkText: "Input something here",   className: "watermark"  }, options);  return this.each(function () {　　　　　　　if ($(this).val().length == 0 || $(this).val() == settings.watermarkText) {   　　//init, set watermark text and class   　　$(this).val(settings.watermarkText).addClass(settings.className);　　　　　　 }   //if blur and no value inside, set watermark text and class again.   $(this).blur(function () {    if ($(this).val().length == 0) {     $(this).val(settings.watermarkText).addClass(settings.className);    }   });   //if focus and text is watermrk, set it to empty and remove the watermark class   $(this).focus(function () {    if ($(this).val() == settings.watermarkText) {     $(this).val('').removeClass(settings.className);    }   });  });   }})(jQuery); 

<div class="search_box"> <input id="tb_search" type="text" /></div><script type="text/javascript"> $(document).ready(function () {  $("#tb_search").watermark({   watermarkText: "站內檢索",   className: "watermark",  }); });</script>