Function getBase64ImageHeader

getBase64ImageHeader(
    str:
        | `data:image/gif;base64,${string}`
        | `data:image/jpeg;base64,${string}`
        | `data:image/jpg;base64,${string}`
        | `data:image/png;base64,${string}`
        | `data:image/svg+xml;base64,${string}`
        | `data:image/webp;base64,${string}`,
): | "data:image/gif;base64,"
| "data:image/jpeg;base64,"
| "data:image/jpg;base64,"
| "data:image/png;base64,"
| "data:image/svg+xml;base64,"
| "data:image/webp;base64,"
get the header of a base64 image.
Parameters
- str:
      | `data:image/gif;base64,${string}`
      | `data:image/jpeg;base64,${string}`
      | `data:image/jpg;base64,${string}`
      | `data:image/png;base64,${string}`
      | `data:image/svg+xml;base64,${string}`
      | `data:image/webp;base64,${string}`
Returns
    | "data:image/gif;base64,"
    | "data:image/jpeg;base64,"
    | "data:image/jpg;base64,"
    | "data:image/png;base64,"
    | "data:image/svg+xml;base64,"
    | "data:image/webp;base64,"
Example
```
import { assertEquals } from "jsr:@std/assert"

const
	img_uri = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAD...",
	img_header = getBase64ImageHeader(img_uri)

assertEquals(img_header, "data:image/png;base64,")
```
- Defined in work/kitchensink_ts/kitchensink_ts/src/image.ts:85