チェックボックスでcontextメニュー表示
context_menu.js

 function contextMenuClick(event) {
   var target = $(event.target);
   var lastSelected;
   //20150827 add-start
     if( window.confirm('context menu show?')){
       contextMenuRightClick(event);
     return;
   } 
   //20150827 add-end