Guards the value to be an instance of the given constructor.

const guardInstance = <
  Obj extends object,
  Payload extends object = object
  value: Obj,
  constructor: Constructor<Obj>,
  callback?: ResultCallback<Obj, { ctor: typeof constructor } & Payload>,
  payload?: Payload
): value is Obj => isInstance(value, constructor, callback, payload);

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.


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 guardInstance() function from which it captures its value.


value: Obj

An object of a generic type variable Obj to guard and be compared with an instance of a given constructor.

constructor: Constructor<Obj>

A class or function that specifies the type of the Constructor.

callback?: ResultCallback<Obj, { ctor: typeof constructor } & 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 ctor property under which is set given constructor, 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 the type captured from the provided value.


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

Example usage

// Usage example.
import { guardInstance } from '@angular-package/type';

// Person interface.
interface Person {
  firstName?: string;
  surname?: string;
  age?: number;
  sex?: 'male' | 'female';

// Class constructor.
class Persons implements Person {
  firstName = '';
  surname = '';
  age = 15;

// Function person constructor.
function personFunctionConstructor(this: Person, ...args: any[]): Person {
  if (args) {
    this.firstName = args[0];
    this.surname = args[1];
    this.age = args[2]; = args[3];
  return this;

const personInstance: Person = new (personFunctionConstructor as any)('First name', 'Sur name', 27);
const personsInstance: Persons = new Persons();

guardInstance(personInstance, personFunctionConstructor as any); // true
guardInstance(personsInstance, Persons); // true

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