# concat

> **Function** in `@langchain/core`

📖 [View in docs](https://reference.langchain.com/javascript/langchain-core/utils/stream/concat)

## Signature

```javascript
concat<T extends unknown>(first: T, second: T): T
```

## Parameters

| Name | Type | Required | Description |
|------|------|----------|-------------|
| `first` | `T` | Yes |  |
| `second` | `T` | Yes |  |

## Returns

`T`

---

[View source on GitHub](https://github.com/langchain-ai/langchainjs/blob/2a5713dfbc5987fb1dcf85cd1de9379816688927/libs/langchain-core/src/utils/stream.ts#L148)