@studnicky/v8/object-spread

Disallows an object spread or Object.assign({}, source) only when the resulting object is assigned directly to this.property or initializes a non-computed class field at construction time. It also disallows Object.assign(this, source) at construction time, because that operation merges an unconstrained key set directly onto the instance. Construction time includes the constructor and a regular method or arrow-valued class field that the constructor calls through this.

The rule leaves a purely local spread alone because it does not reach the constructed instance. At 5,000,000 calls on Node v24, creating a direct object literal took 1.93 ms and creating the equivalent object with a spread took 109.43 ms, a 56.7x difference. Object.assign(this, source) has the additional hidden-class hazard: different source keys cause the instance's own map to diverge across constructions.

Fixable: No · Options: No · Suggested severity: error

✗ Incorrect

class Settings {
  public bag: Record<string, string>;

  public constructor(extra: Record<string, string>) {
    this.bag = { ...extra };
  }
}

class Settings {
  public constructor(extra: Record<string, string>) {
    Object.assign(this, extra);
  }
}

✓ Correct

class Settings {
  public enabled: boolean;
  public retries: number;

  public constructor(extra: { readonly enabled?: boolean; readonly retries?: number }) {
    this.enabled = extra.enabled ?? false;
    this.retries = extra.retries ?? 3;
  }
}

class Settings {
  public tag: string;

  public constructor(extra: Record<string, string>) {
    this.tag = 'settings';
    const local = { ...extra };
    console.log(local);
  }
}