# vue: GTFunction
URL: https://generaltranslation.com/en-GB/docs/vue/reference/types/gt-function.mdx
---
title: GTFunction
description: Describes the synchronous callback used for Vue plain-string catalogue lookups. API reference for GTFunction.

---

The callback returned by [`useGT()`](/docs/vue/reference/composables/use-gt) and the module-level [`t()`](/docs/vue/reference/functions/t) export share this signature. Their state ownership and availability differ, but their lookup result is the same.

## Overview [#overview]

```ts
type GTFunction = (
  message: string,
  options?: GTStringOptions
) => string;
```

| Parameter             | Description                                  | Type                                                             | Optional | Default |
| --------------------- | -------------------------------------------- | ---------------------------------------------------------------- | -------- | ------- |
| [`message`](#message) | Source string to translate.                  | `string`                                                         | No       | —       |
| [`options`](#options) | Optional context used in the catalogue hash. | [`GTStringOptions`](/docs/vue/reference/types/gt-string-options) | Yes      | `{}`    |

## Parameters [#parameters]

### `message`

**Type** `string` · **Required**

The literal source text used to calculate a plain `STRING` hash. Braces remain part of that text; they are not interpolation placeholders.

### `options`

**Type** [`GTStringOptions`](/docs/vue/reference/types/gt-string-options) · **Optional** · **Default** `{}`

Only `$context` is supported. It distinguishes between identical source strings.

## Return value [#returns]

**Type** `string`

Returns the string value from the active catalogue for the calculated hash. If the entry is missing or the catalogue value is not a string, returns `message` unchanged.

The lookup is synchronous and does not perform network operations, ICU processing, or interpolation.

## Implementations [#implementations]

| API                                                 | State source                                                                                                  | Locale updates                                                                                                                             |
| --------------------------------------------------- | ------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------ |
| [`useGT()`](/docs/vue/reference/composables/use-gt) | The [`GTPlugin`](/docs/vue/reference/types/gt-plugin) installed on the current Vue app.                       | Call the callback from a template, computed value or reactive effect to rerun after a reactive plugin changes locale or loads a catalogue. |
| [`t()`](/docs/vue/reference/functions/t)            | The browser-global runtime created by [`initializeGTSPA()`](/docs/vue/reference/functions/initialize-gt-spa). | Module-level results update only after the SPA locale setter reloads the page and modules are evaluated again.                             |

Calling [`useGT()`](/docs/vue/reference/composables/use-gt) without an installed plugin throws when the composable tries to access state. Calling [`t()`](/docs/vue/reference/functions/t) on the server or before SPA initialisation is complete also throws.

## Example [#example]

```ts
import type { GTFunction } from 'gt-vue';

function translateNavigation(gt: GTFunction) {
  return {
    home: gt('Home'),
    settings: gt('Settings'),
  };
}
```