Fields with arbitrarily scoped privacy

_private-fields-faq.md

Fields with arbitrarily scoped privacy

Info on private fields: http://2ality.com/2017/07/class-fields.html

Q&A

• Why the prefix #?
  • You define keys and these keys additionally work completely differently from property keys.
• Is the keyword private necessary?
  • It could be omitted (first mention declares), but I like the distinction between declaration and mention.

friend-fields-oop.js

// Can only be used within this scope
private #data;

class StringBuilder {
  // Accessible within this scope
  #data = '';
  add(str) {
    this.#data += str;
  }
}

function toString(sb) {
  return this.#data;
}

private-fields-fp.js

// Can only be used within this scope
private #data;

function create() {
  return {
    // Only accessible within this scope
    #data: '',
  };
}
function add(sb, str) {
  sb.#data += str;
}
function toString(sb) {
  return sb.#data;
}

private-fields-oop.js

class StringBuilder {
  private #data = '';
  add(str) {
    this.#data += str;
  }
  toString() {
    return this.#data;
  }
}