---
url: /reference/api/Function.mergeConfig.md
---
# Function: mergeConfig()

## Call Signature

```ts
function mergeConfig(defaults, ...overrides): UserConfig
```

Defined in: [src/config/options.ts:369](https://github.com/rolldown/tsdown/blob/a99879ec8d861be3a0ad876930e4eb90d0b8cbc6/src/config/options.ts#L369)

### Parameters

#### defaults

[`UserConfig`](Interface.UserConfig.md)

#### overrides

...[`UserConfig`](Interface.UserConfig.md)\[]

### Returns

[`UserConfig`](Interface.UserConfig.md)

## Call Signature

```ts
function mergeConfig(defaults, ...overrides): InlineConfig
```

Defined in: [src/config/options.ts:373](https://github.com/rolldown/tsdown/blob/a99879ec8d861be3a0ad876930e4eb90d0b8cbc6/src/config/options.ts#L373)

### Parameters

#### defaults

[`InlineConfig`](Interface.InlineConfig.md)

#### overrides

...[`InlineConfig`](Interface.InlineConfig.md)\[]

### Returns

[`InlineConfig`](Interface.InlineConfig.md)