增加千分号，整数自动补零，小数保留两位且不四舍五入

function semicolon_Add(num){
          num = num.replace(/,/g,"");
          if (num != ""){        
              var re = /^\d+(\.\d+)?$/;
              if(re.test(num)){
                  var parts = num.toString().split(".");
                  parts[0] = parts[0].replace(/\B(?=(\d{3})+(?!\d))/g, ",");
                  if(parts.length==1){
                      num =parts[0]+'.00';
                  }else if(parts[1].length>=2){
                      num =parts[0]+"."+parts[1].substring(0,2);
                  }else {
                      num = parts[0]+"."+parts[1]+'0'
                  }            
              }        
          }
          return num;
      }