Guards the value to be an object of generic type variable Obj that contains the given key.

const guardObjectKey = <
  Obj extends object,
  Key extends keyof Obj,
  Payload extends object = object
  value: Obj,
  key: Key,
  callback?: ResultCallback<Obj, { key: typeof key } & Payload>,
  payload?: Payload
): value is Obj => isObjectKey(value, key, callback, payload as any);

Code on GitHub.

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 key 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 guardObjectKey() 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 the given key to guard.

key: Key

A key of generic type variable Key as the property name that the given value contains.

callback?: ResultCallback<Obj, { key: typeof key } & 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 key property given in the key 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 is Obj

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 of a generic Obj that contains the given key.

Example usage

// Example usage.
import { guardObjectKey } 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;

guardObjectKey(OBJECT_ONE, 1030405027); // true, value is ObjectOne
guardObjectKey(OBJECT_ONE, SYMBOL_NUMBER); // true, value is ObjectOne
guardObjectKey(OBJECT_ONE, STRING); // true, value is ObjectOne
// Getter found in the object.
guardObjectKey(OBJECT_ONE, NUMBER); // true, value is ObjectOne

// Searching in an instance of `Class`.
class Class {
  get [NUMBER](): number {
    return NUMBER;
const CLASS = new Class();
// Getter not found.
guardObjectKey(CLASS, NUMBER); // false, value is Class

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