Guards the value to be string type or String instance of a specified length.

const guardStringLength = <
  Type extends AnyString,
  Length extends number,
  Payload extends object = object
  value: Type,
  length: Length,
  callback?: ResultCallback<Type, { length: Length } & Payload>,
  payload?: Payload
): value is StringOfLength<Length, Length, Type> =>
  isStringLength(value, length, callback, payload);

Generic type variables


A generic type variable Obj constrained by AnyString indicates captured string type of the given value via the return type and the value parameter of the provided callback function ResultCallback type.


A generic type variable Length constrained by the number type, by default of value captured from the supplied length indicates the payload parameter type of the provided callback function ResultCallback type and the length of the provided value via the return 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 guardStringLength() function from which it captures its value.


value: Type

The value of a generic type variable Type constrained by AnyString, by default of the type captured from itself to guard.

length: Length

The length of generic type variable Length of a given value.

callback?: ResultCallback<Type, { length: Length } & 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 given callback function consists of the length property of the given length, and it can't be overwritten by the given payload parameter of the main 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 StringOfLength<Length, Length, Type>

The return type is a boolean as the result of its statement, indicating the value is a generic type StringOfLength that takes generic type variable Min and Max(from the provided length parameter) as the length of the supplied value, and Type as the type of the supplied value.


The return value is a boolean indicating whether the value is a string type or an instance of String of a specified length.

Example usage

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

// true; return type `value is StringOfLength<11, 11, "not my name">`
guardStringLength('not my name', 11);
// false; return type `value is StringOfLength<10, 10, "not my name">` 
guardStringLength('not my name', 10);
// false; return type `value is StringOfLength<12, 12, "not my name">`
guardStringLength('not my name', 12);

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