Get FormControl name

validator.component.ts

/**
   * Extract control name from formGroup
   *
   * @return string
   */
  public getControlName(): string {
    let controlName = null;
    const parent = this.control['parent'];

    if (parent instanceof FormGroup) {
      for (const name in parent.controls) {
        if (this.control === parent.controls[name]) {
          controlName = name;
        }
      }
    }

    return controlName;
  }