How to declare local function inside ES6 class?

Question

I have a function that can be used only inside a class and don't want it to be accessible outside the class.

class Auth {
  /*@ngInject*/
  constructor($http, $cookies, $q, User) {
    this.$http = $http;
    this.$cookies = $cookies;
    this.$q = $q;
    this.User = User;

    localFunc(); // Need to create this function, and need it to be accessible only inside this class
  }
}

What I have done so far is declaring the function outside the class

function localFunc() {
  return 'foo';
}
class Auth {
  ...
}

However, this's not good as it pollutes the global function, except I wrapped it inside IIFE. So, is there somehow I can create a local function inside a ES6 class?

Answer 1

No, there is no way to declare local functions in a class. You can of course declare (static) helper methods and mark them as "private" using underscore prefixes, but that's probably not what you want. And you can always declare the local function inside of a method.

But if you need it multiple times then the only way to go is to place it next to the class. If you are writing a script, an IEFE will be necessary as usual. If you're writing an ES6 module (which is the preferred solution), privacy is trivial: just don't export the function.

Answer 2

You could use a Symbol:

const localFunc = Symbol();
class Auth {
  /*@ngInject*/
  constructor($http, $cookies, $q, User) {
    this.$http = $http;
    this.$cookies = $cookies;
    this.$q = $q;
    this.User = User;

    this[localFunc] = function() {
      // I am private
    };
  }
}