code: function fillArray(low, high, step, def) {
              step = step || 1;
              var i = [], x;
              for (x = low; x <= high; x += step) {
                  i[x] = def === undefined ? x : (typeof def === 'function' ? def(x) : def);
              }
              return i;
          }
docs: more heavyweight version than fillArray defined in intf.js