# ★ isString()

## `isString()`

Checks if [`any`](https://www.typescriptlang.org/docs/handbook/basic-types.html#any) value is a [`string`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String) type(by using the [`isStringType()`](/is/isstringtype.md)) or an instance of [`String`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String) by using the [`isStringObject()`](/is/isstringobject.md) function.

{% code title="is-string.func.ts" %}

```typescript
const isString = <
  Type extends AnyString = string,
  Payload extends object = object
>(
  value: any,
  callback: ResultCallback<any, Payload> = resultCallback,
  payload?: Payload
): value is Type =>
  callback(isStringType(value) || isStringObject(value), value, payload);
```

{% endcode %}

### Generic type variables

#### <mark style="color:green;">**`Type`**</mark>**`extends`**<mark style="color:green;">**`AnyString`**</mark>**`=`**<mark style="color:green;">**`string`**</mark>

A generic type variable `Type` constrained by [`AnyString`](/type/anystring.md) indicates [`string`](https://www.typescriptlang.org/docs/handbook/basic-types.html#string) type of the given [`value`](#value-any) via the [return type](#return-type), by default [`string`](https://www.typescriptlang.org/docs/handbook/basic-types.html#string).

#### <mark style="color:green;">**`Payload`**</mark>**`extends`**<mark style="color:green;">**`object`**</mark>**`=`**<mark style="color:green;">**`object`**</mark>

The `Payload` generic type variable constrained by [`object`](https://www.typescriptlang.org/docs/handbook/basic-types.html#object) indicates the type of optional parameter [`payload`](/type/resultcallback.md#payload-payload) of the supplied [`callback`](#callback-resultcallback-less-than-any-payload-greater-than) function and [`payload`](#payload-payload) optional parameter of the [`isString()`](#isstring) function from which it captures its value.

### Parameters

#### `value: any`

The value of [`any`](https://www.typescriptlang.org/docs/handbook/2/everyday-types.html#any) type to check.

#### `callback: ResultCallback<any, Payload>`

A callback `function` of [`ResultCallback`](/type/resultcallback.md) type with parameters, the [`value`](#value-any) that has been checked, the [`result`](/type/resultcallback.md#result-boolean) of this check, and [`payload`](/type/resultcallback.md#payload-payload) of generic type variable [`Payload`](#payloadextendsobject-object) with optional properties from the provided [`payload`](#payload-payload), to handle them before the [`result`](/type/resultcallback.md#result-boolean) return. By default, it uses [`resultCallback()`](/helper/resultcallback.md) function.

#### `payload?: Payload`

An optional [`object`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object) of the generic type variable [`Payload`](#payloadextendsobject-object) is assigned to the [`payload`](/type/resultcallback.md#payload-payload) of the given [`callback`](#callback-resultcallback-less-than-any-payload-greater-than) function.

### Return type

#### `value is Type`

The **return type** is a [`boolean`](https://www.typescriptlang.org/docs/handbook/basic-types.html#boolean) as the result of its statement indicating the [`value`](#value-any) is a generic type variable [`Type`](#typeextendsanystring-string) by default equal to the [`string`](https://www.typescriptlang.org/docs/handbook/basic-types.html#string).

### Returns

The **return value** is a [`boolean`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean) indicating whether the provided [`value`](#value-any) is a [`string`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String) type or an instance of [`String`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String).

## Example usage

```typescript
// Example usage.
import { isString } from '@angular-package/type';

isString('age'); // true; The return type `value is string`
isString(new String('age')); // true; The return type `value is string`

// Fake string example.
const fakeString = new Number('asd');

Object.assign(fakeString, {
  get [Symbol.toStringTag](): string {
    return 'string';
  },
});

isString(fakeString); // false
typeOf(fakeString); // "string"
typeof fakeString; // "object"
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://type.angular-package.dev/is/isstring.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.