protocol.js

/**
 * Extend a constructor/type with new methods
 *
 * @param {Constructor} type         - reference to a constructor
 * @param {Constructor} protocolType - reference to a constructor
 * @param {object} properties        - which stores the method/property names
 * and values
 *
 * @returns {Constructor} reference which equals the type Constructor
 */
function extendType(type, protocolType, properties) {

  // check if required protocol methods are all defined
  let notDefined = Object.getOwnPropertyNames(protocolType.prototype).filter(prop => {
    return !Boolean(properties[prop]);
  });

  if (notDefined.length > 0) {
    throw `missing methods for type extensions of ${type.name} with ${protocolType.name}: ${notDefined.join(' ')}`;
  }

  Object.keys(properties).forEach(property => {
    let value = properties[property];

    if (type.prototype[property]) {
      throw `${property} alread defined on ${type.name} prototype`;
    }

    type.prototype[property] = value;

  });

  return type;
}

/**
 * Creates static methods on the protocol Constructor
 *
 * @param {Constructor} which represents a protocol
 *
 * @returns {Constructor} same
 */
function generateProtocolMethods(protocol) {
  return Object.getOwnPropertyNames(protocol.prototype).forEach(prop => {
    protocol[prop] = (instance, ...args) => {
      return instance[prop].apply(instance, args);
    };
  });

  return protocol;
}

module.exports = {
  extendType,
  generateProtocolMethods
};

test.js

const extendType        = require('./protocol').extendType;
const protocolFunctions = require('./protocol').protocolFunctions;



class Fileable {

  read(){}

  write(){}

}

generateProtocolMethods(Fileable);

class File {
}

extendType(File, Fileable, {

  read(item) {
    return 'i can read';
  },

  write(items) {
    return 'i can write';
  }

});

const f = new File();

console.log(f.read());
console.log(f.write());

console.log('and now for the static methods');

console.log(Fileable.read(f));
console.log(Fileable.write(f));

module.exports = File;