Preview

Preview opens PrintLink's preview window so the user can see what is about to print. What the window shows is what the printer receives — confirming does not re-render, which rules out preview-versus-print mismatches by construction.

const session = await client
  .compose({ queueId })
  .paper('A4')
  .addPdf(bytes)
  .preview();

console.log(session.pageCount);      // how many pages
console.log(session.warnings);       // option downgrades, if any

Requires the job.preview permission (granted by default). PrintLink opens the window and the user prints from there; your page can also drive it:

await client.previewPrint(session.previewSessionId);   // print what is previewed
await client.previewClose(session.previewSessionId);   // close it

What is in the window

• Thumbnails on the left, one per output page, with a source badge for mixed content (image / PDF / web page / template).
• Status bar, e.g. 12 output pages · 4 sources · A4 210×297 mm.
• Options panel: paper, copies, duplex, colour, quality — changing one takes effect immediately and re-renders the preview.
• Canvas actions when an image page is selected: drag, scale, rotate, flip and "Reset this image".

Output pages and source items are different things: output pages are the pages of the final artefact (1 to pageCount), while source items are the pieces you added. A 3-page PDF in a mixed job is 1 source item covering 3 output pages. Badges and the status bar's "sources" refer to the latter.

Changing the preview from code

The window handles user changes on its own; your page usually does not need to intervene. When it does, use previewUpdate:

await client.previewUpdate({
  previewSessionId: session.previewSessionId,
  options: { paper: { id: 'A5' } },     // options is replaced, not merged
});

Page by page

If you build your own preview UI instead of using the desktop window, pull rasters one page at a time:

const page = await client.previewGetPage(session.previewSessionId, 0);
// page.pngBase64      the page bitmap
// page.origin         where it came from: { itemIndex, kind, itemPageIndex }
// page.pageLayout     the layout actually used, always present

session.source.items maps each source to its output pages (outputPageStart / outputPageCount), which is exactly what you need for a caption like "page 3 · PDF 2/3".

Closing and expiry

• Closing the window or pressing Esc hides it first and recycles the session asynchronously; it never lands on an "expired preview" screen.
• A session that sits unused expires, after which previewPrint / previewGetPage return PREVIEW_NOT_FOUND.
• previewClose releases it eagerly, which is tidier when a page navigates away.

See also