---
url: https://node-ts.github.io/bus/api/bus-messages/functions/defineCommand.md
---
[API reference](../../index.md) / [@node-ts/bus-messages](../index.md) / defineCommand

# Function: defineCommand()

```ts
function defineCommand<TName>(name, options?): <TData>() => MessageDefinition<DefinedMessage<TName, TData>, TData>;
```

Defined in: [packages/bus-messages/src/define-command.ts:29](https://github.com/node-ts/bus/blob/2e6cf65c27833b707ae31ee623cfb6343770f434/packages/bus-messages/src/define-command.ts#L29)

Declares a command, an instruction sent to one handler, without writing a class. The definition
creates commands from their fields, and is used anywhere a message class is: `handlerFor`,
`startedBy` and `when`. The commands it creates are plain objects, with `$name` and `$version`
added.

The name comes first and the fields second, so the name's literal type is inferred. Run
`bus generate-message-types` (in `@node-ts/bus-cli`) to have Dates, Maps, Sets, bigints and classes
in the fields restored when the command is received.

## Type Parameters

| Type Parameter |
| ------ |
| `TName` *extends* `string` |

## Parameters

| Parameter | Type | Description |
| ------ | ------ | ------ |
| `name` | `TName` | the `$name` of the command, which routes it, so make it unique |
| `options?` | [`DefineMessageOptions`](../interfaces/DefineMessageOptions.md) | the `$version` of the command's contract |

## Returns

a function that takes the type of the command's fields as its type argument, and returns
the definition

<`TData`>() => [`MessageDefinition`](../interfaces/MessageDefinition.md)<[`DefinedMessage`](../type-aliases/DefinedMessage.md)<`TName`, `TData`>, `TData`>

## Example

```ts
export const PlaceOrder = defineCommand('@my-org/orders/place-order')<{
  orderId: string
  placedAt: Date
}>()
export type PlaceOrder = MessageOf<typeof PlaceOrder>

await bus.send(PlaceOrder({ orderId: '1', placedAt: new Date() }))
handlerFor(PlaceOrder, async placeOrder => placeOrder.placedAt.getTime())
```