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

## Call Signature

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

Defined in: [src/config/options.ts:367](https://github.com/rolldown/tsdown/blob/eb40c95efdf7f98d0aa7b0178a3b7322986bd419/src/config/options.ts#L367)

### 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:371](https://github.com/rolldown/tsdown/blob/eb40c95efdf7f98d0aa7b0178a3b7322986bd419/src/config/options.ts#L371)

### Parameters

#### defaults

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

#### overrides

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

### Returns

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