Checks if any value is an instance of a given constructor.

const isInstance = <Obj, Payload extends object>(
  value: any,
  constructor: Constructor<Obj>,
  callback: ResultCallback<
    { ctor: typeof constructor } & Payload
  > = resultCallback,
  payload?: Payload
): value is Obj =>
    isObject(value) &&
      typeof constructor === 'function' &&
      constructor instanceof Function
      ? value instanceof constructor
      : false,
    { ...payload, ctor: constructor } as any

Generic type variables


A generic type variable Obj, by default captured from the provided constructor, indicates the type of generic type Constructor, and the type of value parameter 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 isInstance() function from which it captures its value.


value: any

The value of any type to be an instance of a given constructor.

constructor: Constructor<Obj>

A class or function that specifies the type of Constructor.

callback: ResultCallback<any, { ctor: typeof constructor } & 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 ctor property given in the constructor 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 of type captured from the supplied constructor.


The return value is a boolean indicating whether the provided value is an instance of a given constructor.

Example usage

Basic usage

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

// Classes.
class Some { x = 127; }
class Two { y = 'Lorem ipsum'; }

const SOME = new Some();
const TWO = new Two();

isInstance(TWO, Some); // false
isInstance(SOME, Some); // true
isInstance<Some, object>(TWO, Two); // true and type error

isInstance(new Array(), Array), // Returns `true` as `value is Array`
isInstance(new Boolean(), Boolean), // Returns `true` as `value is Boolean`
isInstance(new Date(), Date), // Returns `true` as `value is Date`
isInstance(new Error(), Error), // Returns `true` as `value is Error`
isInstance(new Function(), Function), // Returns `true` as `value is Function`
isInstance(new Map(), Map), // Returns `true` as `value is Map`
isInstance(new Number(), Number), // Returns `true` as `value is Number`
isInstance(new Object(), Object), // Returns `true` as `value is Object`
isInstance(new RegExp(/^[]/), RegExp), // Returns `true` as `value is RegExp`
isInstance(new Set(), Set), // Returns `true` as `value is Set`
isInstance(new String(), String), // Returns `true` as `value is String`

Parameters callback and payload

// Example usage with callback and payload.
import { isInstance } from '@angular-package/type';

// Classes.
class Some { x = 127; }
class Two { y = 'Lorem ipsum'; }

const SOME = new Some();
const TWO = new Two();

isInstance(TWO, Some, (result, value, payload) => {
  value // Returns the provided `Two`
  if (payload) {
    payload.className // Returns `'Some'`
    payload.ctor // Returns the provided `Some`
  return result;
}, { className: Some });

Function constructor

// Example usage with function constructor.
import { isInstance } from '@angular-package/type';

// Function constructor.
function functionConstructor(this: any, ...args: any[]): any {
  if (args) {
    args.forEach((arg, index: number) => this[index] = arg[index]);
  return this;

const anyInstance: any = new (functionConstructor as any)('First name', 'Sur name', 27);
isInstance(anyInstance, functionConstructor as any); // true

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