encapsulation.md

[JavaScript] - Encapsulation

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There are 2 ways to achieve Encapsulation in JS:

• Protected Properties and Methods: coding convention (not true private), use _ before a property to notify other developer this property is protected and should not be used directly.
• Private Class Fields and Methods: languague feature that is still under proposal, might not work for every browser and are subjected to syntax change.

// 1) Public fields
// 2) Private fields
// 3) Public methods
// 4) Private methods
// (there is also the static version)

class Account {
  // 1) Public fields (only in the instances, not in the prototype)
  locale = navigator.language;

  // 2) Private fields (only in the instances, not in the prototype)
  #movements = [];
  #pin;

  constructor(owner, currency, pin) {
    this.owner = owner;
    this.currency = currency;
    this.#pin = pin;

    // Protected property.
    // this._movements = [];
    // this.locale = navigator.language;

    console.log(`Thanks for opening an account, ${owner}`);
  }

  // 3) Public methods

  // Public interface
  getMovements() {
    return this.#movements;
  }

  deposit(val) {
    this.#movements.push(val);
    return this;
  }

  withdraw(val) {
    this.deposit(-val);
    return this;
  }

  requestLoan(val) {
    // if (this.#approveLoan(val)) {
    if (this._approveLoan(val)) {
      this.deposit(val);
      console.log(`Loan approved`);
      return this;
    }
  }

  static helper() {
    console.log('Helper');
  }

  // 4) Private methods
  // #approveLoan(val) { // haven't worked yet with Chrome
  _approveLoan(val) {
    return true;
  }
}

const acc1 = new Account('Jonas', 'EUR', 1111);

// acc1._movements.push(250);
// acc1._movements.push(-140);
// acc1.approveLoan(1000);

acc1.deposit(250);
acc1.withdraw(140);
acc1.requestLoan(1000);
console.log(acc1.getMovements());
console.log(acc1);
Account.helper();

// console.log(acc1.#movements);
// console.log(acc1.#pin);
// console.log(acc1.#approveLoan(100));

// Chaining
acc1.deposit(300).deposit(500).withdraw(35).requestLoan(25000).withdraw(4000);
console.log(acc1.getMovements());