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

---
```ts
$field(
   ctx, 
   target, 
   fieldIndex): void
```

Decorate a model property with a field index. Field indices are required for all fields of emitted messages.

## Parameters

| Parameter | Type | Description |
| :------ | :------ | :------ |
| `ctx` | `DecoratorContext` | - |
| `target` | `ModelProperty` |  |
| `fieldIndex` | `number` |  |

## Returns

`void`
