optional(element)this
$.validator.addMethod("check_invoiceNo",function(value,element,params){ var check = /\d{6,15}$/; return this.optional(element)||(check.test(value)); },"*只容許8-15位數字!");
optional(element) 用於表單控件的值不爲空時才觸發驗證,若是值爲空也要觸發則移除this.optional(element)。code