Checks if any value is an object(by using the isObject()) function with its key of the PropertyKey type.

The function uses the hasOwnProperty() method of Object to find enumerable and non-enumerable PropertyKey as string, number, symbol unlike Object.keys() that finds only enumerable property names excluding symbol, but it can't find getter accessor unlike in operator, which can. To find also getter accessors use the isObjectKeyIn() function.

const isObjectKey = <
  Obj extends object,
  Payload extends object = object
  value: any,
  key: PropertyKey,
  callback: ResultCallback<any, { key: typeof key } & Payload> = resultCallback,
  payload?: Payload
): value is Obj =>
    isObject(value) ? {}, key) : false,
    { ...payload, key } as any

Generic type variables


A generic type variable Obj indicates the type of value parameter by default object via the return type value is 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 isObjectKey() function from which it captures its value.


value: any

The value of any type to check against an object that contains a key from a given key.

key: PropertyKey

A property key to check if a given value contains.

callback: ResultCallback<any, { key: typeof key } & Payload>

A 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 parameter of the core function, and it can't be overwritten by the given payload parameter of the core 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 a generic type variable Obj by default equal to the object.


The return value is a boolean indicating whether the provided value is an object with its key.

Example usage

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

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

interface ObjectOne {
  'key as string'?: boolean;
  1030405027?: string;
  5?: string;
  [NUMBER]: number;
  [STRING]: string;
  [SYMBOL_NUMBER]?: string;
  [SYMBOL_STRING]?: number;
  x: number;
const OBJECT_ONE: ObjectOne = {
  'key as string': true,
  1030405027: 'key is number',
  5: 'key is also number',
  [STRING]: 'key is string',
  [SYMBOL_NUMBER]: 'key is symbol number',
  x: 3000
isObjectKey(OBJECT_ONE, STRING); // true
isObjectKey(OBJECT_ONE, 1030405027); // true
isObjectKey(OBJECT_ONE, NUMBER); // true
isObjectKey(OBJECT_ONE, SYMBOL_NUMBER); // true
isObjectKey(OBJECT_ONE, SYMBOL_STRING); // true

class Class {

  1030405027 = 'my new number';
  5 = 'my number';

  firstName = 'My name';
  surname = 'Surname';

  x = NUMBER;
  y = STRING;

  get [NUMBER](): number {
    return this.x;
  get [STRING](): string {
    return this.y;

  get [SYMBOL_NUMBER](): number {
    return this.x;

  get [SYMBOL_STRING](): string {
    return this.y;

const CLASS = new Class();

// One of the differences between the `in` operator and the `hasOwnProperty()`
// method is that it doesn't find a getter key
isObjectKey(CLASS, SYMBOL_NUMBER); // false
isObjectKey(CLASS, SYMBOL_STRING); // false

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