Checks if the value is not the type obtained from its object class equal to 'undefined', not an undefined type and is not equal to undefined.

const isNotDefined = <Type, Payload extends object = object>(
  value: Type,
  callback: ResultCallback<Type, Payload> = resultCallback,
  payload?: Payload
): value is Undefined<Type> =>
    typeOf(value) === 'undefined' &&
      typeof value === 'undefined' &&
      value === undefined,

Generic type variables


A generic type variable Type indicates the captured type of the given value via the return type value is Undefined<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 isNotDefined() function from which it captures its value.


value: Type

The value of generic type variable Type, by default of the type captured from itself to check.

callback: ResultCallback<Type, 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.

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 Undefined<Type>

The return type is a boolean as the result of its statement indicating the value is a generic type Undefined that takes a generic type variable Type by default of value captured from the supplied value which changes to never on the captured type undefined.


The return value is a boolean indicating whether the value is not defined, is undefined.

Example usage

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

const anyUndefined: any = undefined;
const firstName = undefined;
const surname = 'My last name ';

isNotDefined(anyUndefined); // true; return type is `value is any`
isNotDefined(firstName); // true;  return type is `value is undefined`
isNotDefined(surname); // false; return type is `value is never`

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