Guards the value to be one of string, number, or symbol type.

const guardKey = <Key extends PropertyKey, Payload extends object>(
  value: Key,
  callback?: ResultCallback<Key, Payload>,
  payload?: Payload
): value is Key => isKey(value, callback, payload);

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Generic type variables


A generic type variable Key constrained by PropertyKey indicates captured 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 guardKey() function from which it captures its value.


value: Key

The value of generic type variable Key to guard.

callback?: ResultCallback<Key, 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 Key

The return type is a boolean as the result of its statement indicating the value is generic type variable Key.


The return value is a boolean indicating whether the value is a string, number, or symbol.

Example usage

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

guardKey('string key'); // true, value is PropertyKey
guardKey(27); // true, value is PropertyKey
guardKey(Symbol('string key')); // true, value is PropertyKey
guardKey(Symbol(27)); // true, value is PropertyKey

guardKey(new String('string key') as any); // false, value is PropertyKey
guardKey(new Number(27) as any); // false, value is PropertyKey

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