Checks if any value is an object(by using the isObject()) with a key of the PropertyKey in it(or its prototype chain) by using the in operator.

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

Generic type variables


A generic type variable Obj indicates the type of value parameter via the return type value is Obj, by default object.


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 isObjectKeyIn() function from which it captures its value.


value: any

The value of any type to check against an object that contains(or its prototype chain) a key from a given key.

key: PropertyKey

A property key to check if a given value contains(or its prototype chain).

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 that contains(or its prototype chain) a given key.

Example usage

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

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

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 `in` operator and the `hasOwnProperty()`
// method is that it finds a getter key
isObjectKeyIn(CLASS, SYMBOL_NUMBER); // true
isObjectKeyIn(CLASS, SYMBOL_STRING); // true

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