js中，为什么要用两个encodeURIComponent，用一个的话为什么是乱码？

Question

var url = context1+"/trade/home/qdmenu/js/appeal_form.jsp?data="+encodeURIComponent(encodeURIComponent(delHtmlTag(data.lABEL_CONTENT),"GBK"));                window.showModalDialog(url,'','status:no;dialogLeft:'+lef+'px;dialogTop:300px;center=yes;dialogWidth:800px;dialogHeight:200px;scroll:no;help:no;');