23.1.3.1 Map.prototype.clear() 23.2.3.2 Set.prototype.clear()
function clear() {
        for (var that = _validateCollection(this, NAME), data = that._i, entry = that._f; entry; entry = entry.n) {
          entry.r = true;
          if (entry.p) entry.p = entry.p.n = undefined;
          delete data[entry.i];
        }
        that._f = that._l = undefined;
        that[SIZE] = 0;
      }