Allow `renderPageAsImage` to return a data URL

[vladiantio]

Describe the feature

I propose enhancing the renderPageAsImage function adding a toDataURL option:

• Introduce a new boolean option, toDataURL, to the options object.
• When options.toDataURL is set to true, the function's return type should be Promise<string>, resolving with the data URL of the rendered page.
• When the option is false or not provided, the function should maintain its existing behavior, returning a Promise<ArrayBuffer>.

This can be achieved with TypeScript overloads to ensure type safety:

// Returns a buffer by default
function renderPageAsImage(
  data: DocumentInitParameters['data'] | PDFDocumentProxy,
  pageNumber: number,
  options?: {
    // ... other options
    toDataURL?: false
  },
): Promise<ArrayBuffer>

// Returns a data URL string when toDataURL is true
function renderPageAsImage(
  data: DocumentInitParameters['data'] | PDFDocumentProxy,
  pageNumber: number,
  options: {
    // ... other options
    toDataURL: true
  },
): Promise<string>

Example Usage:

import { getDocumentProxy, renderPageAsImage } from 'unpdf'

const buffer = await readFile('./document.pdf')
const pdf = await getDocumentProxy(new Uint8Array(buffer))
const pageNumber = 1

// Get the image as a data URL for web embedding
const dataUrl = await renderPageAsImage(pdf, pageNumber, {
  toDataURL: true,
})

// Example: <img src="data:image/png;base64,iVBORw0KGgo...">
const html = `<img src="${dataUrl}">`

// ...

Additional information

• Would you be willing to help implement this feature?

[johannschopplich]

Resolved by #41. Thanks!