Guards the value to be a Function.

const guardFunction = <Type extends Function, Payload extends object>(
  value: Type,
  callback?: ResultCallback<Type, Payload>,
  payload?: Payload
): value is Type => isFunction(value, callback, payload);

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Generic type variables


A generic type variable Type constrained by Function indicates captured function 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 guardFunction() function from which it captures its value.


value: Type

The function of a generic type variable Type to guard.

callback?: ResultCallback<Type, 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 is Type

The return type is a boolean as the result of its statement indicating the value is a generic type variable Type by default equal to the type captured from the supplied value.


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

Example usage

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

guardFunction('x'); // false value is Function
guardFunction(() => {}); // true value is () => void
guardFunction((x: number, y: number) => x + y); // true value is (x: number, y: number) => number

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