code: function(levels) {
        for (var i = 0; i < levels.length; ++i) {
          var level = levels[i];
          for (var j = 0; j < level.length; ++j) {
            if (level[j].factory) {
              _this.injectAndRegister(level[j].name, level[j].factory);
            } else if (level[j].obj) {
              _this.register(level[j].name, level[j].obj);
            }
          }
        }
      }
docs: Given a dependency graph in topological order, assemble it.