Public Mutable Field (ARCH3186)

Key typescript.quality.public-mutable-field · Severity warning · Category quality

Publicly exposed mutable fields break the class’s encapsulation and let outside code assign invalid state. They should be guarded with accessors (getter/setter) or readonly.

Incorrect

class Account {
  public balance: number = 0;
}

const a = new Account();
a.balance = -500; // unguarded access to an invalid state

Correct

class Account {
  private _balance = 0;
  get balance() { return this._balance; }

  deposit(amount: number) {
    if (amount <= 0) throw new Error("invalid");
    this._balance += amount;
  }
}

Fix

Make the field private and manage mutations through validating accessors or methods.