config/defer.js

// Create a deferredConfig prototype so that we can check for it when reviewing the configs later.
function DeferredConfig() {}
DeferredConfig.prototype.prepare = function() {};
DeferredConfig.prototype.resolve = function() {};

// Accept a function that we'll use to resolve this value later and return a 'deferred' configuration value to resolve it later.
function deferConfig(func) {
  var obj = Object.create(DeferredConfig.prototype);
  obj.prepare = function(config, prop, property) {
    var original = prop[property]._original;
    obj.resolve = function() {
      var value = func.call(config, config, original);
      Object.defineProperty(prop, property, {value: value});
      return value;
    };
    Object.defineProperty(prop, property, {get: function() { return obj.resolve(); }});
    return obj;
  };
  return obj;
}

module.exports.deferConfig = deferConfig;
module.exports.DeferredConfig = DeferredConfig;