Guards the value to be undefined.

const guardUndefined = <Payload extends object>(
  value: undefined,
  callback?: ResultCallback<undefined, Payload>,
  payload?: Payload
): value is undefined => isUndefined(value, callback, payload);

Generic type variables


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 guardUndefined() function from which it captures its value.


value: undefined

The value of an undefined type to guard.

callback?: ResultCallback<undefined, 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.

payload?: Payload

An optional object of the generic type variable Payload is assigned to the payload of the given callback function.

Return type

value isundefined

The return type is a boolean as the result of its statement.


The return value is a boolean indicating whether the value is undefined.

Example usage

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

const UNDEFINED: undefined = undefined;

guardUndefined(UNDEFINED); // true; 
guardUndefined('x'); // false; type error
guardUndefined(5); // false; type error

const tracker = {
  error: 'sentry',

const undefinedCallback = <Type, Payload>(
  result: boolean,
  value: Type,
  payload?: typeof tracker & Payload
) => {
  if (payload?.error === 'sentry') {
    // ...
  value; // 5
  result; // false
  payload {
      "name": "guardUndefined",
      "error": "sentry"
  return result;

const gUndefined = (value: undefined): value is undefined =>
  guardUndefined(value, undefinedCallback, tracker);

gUndefined(5 as any); // false

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