Example of setting up expected api from environments using helpers.

helpers.js

var expects = function(config, spec) {
  for(var k in spec) {
    if (config[k] === 'undefined') {
      config[k] = spec[k];
    }
  }
};

var spec = {
  context: function() { return {}; },
  registerHelpers: function() { }
};

module.exports = function (config) {
  expects(config, spec);
  
  Library.addHelper('foo', function (bar) {
    var context = config.context();
    var baz = context[bar] || 'default';
    return 'Hello ' + baz;
  });
};