Guards the value to be an object of a generic type variable Obj with specified keys in it(or its prototype chain).

const guardObjectKeysIn = <
  Obj extends object,
  Key extends keyof Obj,
  Payload extends object = object
  value: Obj,
  keys: Key[],
  callback?: ResultCallback<Obj, { keys: typeof keys } & Payload>,
  payload?: Payload
): value is Obj => isObjectKeysIn(value, keys, callback, payload as any);

Generic type variables


A generic type variable Obj constrained by object indicates captured object type of the given value via the return type and the value parameter of the provided callback function ResultCallback type.

Keyextends keyofObj

A generic type variable Key constrained by the keyof Obj, by default of value captured from the supplied keys indicates the specific property name of Obj.


The Payload generic type variable constrained by object indicates the type of optional parameter payload of the supplied callback function and payload optional parameter of the guardObjectKeysIn() function from which it captures its value.


value: Obj

An object of a generic type variable Obj, by default of the type captured from itself that contains(or its prototype chain) the given keys to guard.

keys: Key[]

An Array of property keys to check whether the given value contains(or its prototype chain).

callback?: ResultCallback<Obj, { keys: typeof keys } & Payload>

The optional callback function of ResultCallback type with parameters, the value that has been checked, the result of this check, and payload of generic type variable Payload with optional properties from the provided payload, to handle them before the result return. By default, it uses resultCallback() function.

The payload parameter of the callback function consists of the keys property given in the keys parameter, and it can't be overwritten by the given payload parameter of the main function.

payload?: Payload

An optional object of the generic type variable Payload is assigned to the payload of the given callback function.

Return type

value isObj

The return type is a boolean as the result of its statement indicating the value is an object of a generic type variable Obj, by default of type captured from the supplied value.


The return value is a boolean indicating whether the value is an object with specified keys in it(or its prototype chain).

Example usage

// Example usage.
import { guardObjectKeysIn } from '@angular-package/type';

const NUMBER = 10304050;
const STRING = '!@#$%^&*()abcdefghijklmnoprstuwyz';
const SYMBOL_NUMBER: unique symbol = Symbol(NUMBER);

interface ObjectOne {
  1030405027?: string;
  [NUMBER]: number;
  [STRING]: string;
  [SYMBOL_NUMBER]?: string;
const OBJECT_ONE: ObjectOne = {
  1030405027: 'key is number',
  [STRING]: 'key is string',
  [SYMBOL_NUMBER]: 'key is symbol number',
  get [NUMBER](): number {
    return NUMBER;

guardObjectKeysIn(OBJECT_ONE, [
  1030405027]); // true, value is Class

// Searching in an instance of `Class`.
class Class {
  get [NUMBER](): number {
    return NUMBER;
const CLASS = new Class();
// Getter found.
guardObjectKeysIn(CLASS, [NUMBER]); // true, value is Class

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