# BaseMime

**Kind:** Type

**Source:** [`src/utils/mime.ts`](https://github.com/honojs/hono/blob/main/src/utils/mime.ts#L33)

**Part of:** [Utils](subsystem-src-utils)

Union types for BaseMime

`BaseMime` is a union type that represents the base MIME values defined in `src/utils/mime.ts`. It constrains APIs and variables that work with those MIME values so callers can pass only members of the union.

## Definition

```ts
(typeof _baseMimes)[keyof typeof _baseMimes]
```

## Diagram

```mermaid
graph LR
  Input[Content-Type value] --> BaseMime[BaseMime]
  BaseMime --> Headers[HTTP headers]
  BaseMime --> Validation[Type-safe MIME handling]
```

## Usage

```ts
import type { BaseMime } from './utils/mime';

function createHeaders(mime: BaseMime) {
  return {
    'Content-Type': mime,
  };
}

declare const mime: BaseMime;

const headers = createHeaders(mime);
```

## AI Coding Instructions

- Import `BaseMime` with `import type` when it is only used as a TypeScript type.
- Use `BaseMime` for function parameters, configuration fields, and header builders that accept base MIME values.
- Keep MIME literals aligned with the union declared in `src/utils/mime.ts`.
- Do not cast arbitrary strings to `BaseMime`; validate external input before passing it to typed APIs.