There is a non-open-source JavaScript decorator library using this. It has many (real) examples, but the one that first comes to mind is its use of the xtype.is

There is a non-open-source JavaScript decorator library using this. It has many (real) examples, but the one that first comes to mind is its use of the xtype.is API method (http://xtype.js.org/api/is http://xtype.js.org/api/is) to perform runtime validations based on validation meta-data that's defined in configuration. For an idea of what that looks like, see: http://xtype.js.org/guide/checking_combinations_of_types http://xtype.js.org/guide/checking_combinations_of_types