Is it possible to give javascript partial class behavior like C# or monkey patching like Ruby does?

Question

The idea behind partial classes is that you can group certain functions together. The best example of this in C# is putting control definitions in one file and the event han

Answer 1

Here is one approach using ES6 and compatible with ES5 using Babel:

In this example I create a MyClass in several files, using three files:

index.js (this is important so you can import the class just via the folder name)

symbols.js (this contains the symbols for private members)

additionalMethods.js (a file that is later attached to the class prototype)

index.js content

import symbols from "./symbols";

export default class MyClass {
  [symbols.existentPrivateMethod]() {
    return "this is the result";
  }
}

import additionalMethod, {anotherAdditionalMethod, additionalPrivateMethod} from "./additionalMethods";
const additionalMethodsObject = {
  additionalMethod: additionalMethod,
  anotherAdditionalMethod: anotherAdditionalMethod
};
additionalMethodsObject[symbols.additionalPrivateMethod] = additionalPrivateMethod;

Object.assign(MyClass.prototype, additionalMethodsObject);

additionalMethods.js contents

import symbols from "./symbols";

export default function additionalMethod() {
  return this[symbols.existentPrivateMethod]();
}

export function anotherAdditionalMethod() {
  return this[symbols.additionalPrivateMethod]();
}

export function additionalPrivateMethod() {
  return "yet another result";
}

symbols.js content

const symbols = {
  existentPrivateMethod: Symbol("myPrivateMethod"),
  additionalPrivateMethod: Symbol("additionalPrivateMethod")
};

export default symbols;

Complete project https://github.com/nicosommi/partialClass

Complete explanation https://nicosommi.com/2015/08/10/partial-class-approach-for-es6/