Snippet

True Runtime Encapsulation with ECMAScript Private Fields

TypeScript's private modifier only performs static checks during compilation, leaving properties visible on runtime objects. Using native ECMAScript private fields prefixed with # guarantees true privacy at runtime in JavaScript engines.

snippet.ts

typescript

class BankAccount {
  #balance: number;
  public readonly accountId: string;
 
  constructor(accountId: string, initialDeposit: number) {
    this.accountId = accountId;
    this.#balance = initialDeposit;
  }
 
  public deposit(amount: number): void {
    if (amount <= 0) throw new Error("Deposit amount must be positive");
    this.#balance += amount;
  }
 
  public getBalance(): number {
    return this.#balance;
  }
}

Breakdown

#balance: number;

Declares a hard private field using the hash prefix, making it inaccessible outside the class even at runtime.

this.#balance += amount;

Accesses and mutates the private field inside instance methods safely.

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True Runtime Encapsulation with ECMAScript Private Fields

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