ExampleConsumer.js

define(
    ['underscore'],
    function (_) {
      // Outputs "true"
      console.log(_.deepClone !== undefined);
    }
);

main.js

require.config({
  map: {
    '*': {
      'underscore': 'underscore-extensions'
    },
    'underscore-extensions': {
      'underscore': 'underscore'
    }
  }
});

underscore-extensions.js

// This is a shim module that adds functionality to Underscore.js that we want to be availabla
// everywhere within our project.

define(
    ['underscore'],
    function (_) {
        // define extra helpers attached to _
        _.deepClone = function () {
          /* ... */
        }

        return _;
    }
);

underscore.js

// This is just the real underscore file.