---
jsApi: true
title: "[F] $extension"

---
```ts
$extension(
   context, 
   entity, 
   extensionName, 
   value): void
```

## Parameters

| Parameter | Type |
| :------ | :------ |
| `context` | `DecoratorContext` |
| `entity` | `Type` |
| `extensionName` | `string` |
| `value` | `TypeSpecValue` |

## Returns

`void`
