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   1  /**
   2   * @provides javelin-view-visitor
   3   * @requires javelin-install
   4   *           javelin-util
   5   *
   6   * Add new behaviors to views without changing the view classes themselves.
   7   *
   8   * Allows you to register specific visitor functions for certain view classes.
   9   * If no visitor is registered for a view class, the default_visitor is used.
  10   * If no default_visitor is invoked, a no-op visitor is used.
  11   *
  12   * Registered visitors should be functions with signature
  13   * function(view, results_of_visiting_children) {}
  14   * Children are visited before their containing parents, and the return values
  15   * of the visitor on the children are passed to the parent.
  16   *
  17   */
  18  
  19  JX.install('ViewVisitor', {
  20    construct: function(default_visitor) {
  21      this._visitors = {};
  22      this._default = default_visitor || JX.bag;
  23    },
  24    members: {
  25      _visitors: null,
  26      _default: null,
  27      register: function(cls, visitor) {
  28        this._visitors[cls] = visitor;
  29      },
  30      visit: function(view, children) {
  31        var visitor = this._visitors[cls] || this._default;
  32        return visitor(view, children);
  33      }
  34    }
  35  });