code: function( n ){
  
          if(!isNaN( this.c[2+n].textContent )){ 
              var nx = this.numValue( this.c[2+n].textContent );
              this.c[2+n].textContent = nx;
              this.value[n] = nx;
          } else { // not number
              this.c[2+n].textContent = this.value[n];
          }
  
      }
docs: ///