# WsParamsFactory

**Kind:** Class

**Source:** [`packages/websockets/factories/ws-params-factory.ts`](https://github.com/nestjs/nest/blob/master/packages/websockets/factories/ws-params-factory.ts#L4)

**Part of:** [Websockets](subsystem-packages-websockets)

`WsParamsFactory` resolves WebSocket handler parameter values from the runtime argument array. It maps WebSocket parameter types—such as the connected socket or message payload—to the values injected into gateway handler methods.

## Methods

| Method | Signature | Returns |
|---|---|---|
| `exchangeKeyForValue` | `exchangeKeyForValue(type: number, data: string | undefined, args: unknown[])` | `void` |

## Where it refuses work

- `WsParamsFactory` stops the work with an early return when `!args`.

## Diagram

```mermaid
graph LR
  A[WebSocket event arguments] --> B[WsParamsFactory.exchangeKeyForValue]
  B --> C{WsParamtype}
  C -->|SOCKET| D[Socket client: args[0]]
  C -->|PAYLOAD| E[Message payload: args[1]]
  E -->|Property key provided| F[Payload property]
```

## Usage

```ts
import { WsParamsFactory } from '@nestjs/websockets/factories/ws-params-factory';
import { WsParamtype } from '@nestjs/websockets/enums/ws-paramtype.enum';

const paramsFactory = new WsParamsFactory();

const client = { id: 'socket-123' };
const payload = { roomId: 'general', message: 'Hello' };
const args = [client, payload];

const socket = paramsFactory.exchangeKeyForValue(
  WsParamtype.SOCKET,
  undefined,
  args,
);

const message = paramsFactory.exchangeKeyForValue(
  WsParamtype.PAYLOAD,
  'message',
  args,
);

console.log(socket); // { id: 'socket-123' }
console.log(message); // "Hello"
```

## AI Coding Instructions

- Treat `args[0]` as the WebSocket client and `args[1]` as the incoming event payload.
- Use `WsParamtype.SOCKET` to resolve the client connection and `WsParamtype.PAYLOAD` to resolve the full payload or a payload property.
- Pass a payload property key only when extracting a nested top-level value; omit it to receive the complete payload.
- Keep parameter-resolution behavior aligned with WebSocket decorators such as `@ConnectedSocket()` and `@MessageBody()`.
- Avoid depending on this factory as a general-purpose object accessor; it is intended for WebSocket handler argument binding.

## Relationships

- IMPORTS → `isFunction`