Callbacks

Six places where the SDK hands you a decision or a job of its own — a dialog to replace, a link to open, a question to answer. Callbacks decide; events observe. Everything that merely happened — the page, the zoom, the tool, a field edited, entered or left, an error, a signature or stamp saved — is an event on viewer.on(...), so any number of parts of your page can listen, and each can stop on its own: see Events. The last four callbacks are how you replace or extend the SDK's own dialogs — see What you can replace.

CallbacksConfigconfig.callbacks

Example

viewer.tsTypeScript

const viewer = new PDFViewer(container, doc, {
  callbacks: {
    onDownload: async () => {
      const presignedUrl = await fetchPresignedUrl(); // your API
      const exporter = viewer.createExporter();
      const res = await exporter.uploadTo(presignedUrl, { method: 'PUT' });
      if (!res.ok) showError(res.status); // uploadTo does not reject on an HTTP error
    },
    onExternalLink: (url) => {
      if (confirm('Open ' + url + '?')) window.open(url, '_blank', 'noopener,noreferrer');
    },
  },
});

Options 6

onDownload() => void

Takes over the toolbar Download button (after forms.validateRequired). When set, the SDK's Download dialog and flow do not run; your function does — get the bytes from viewer.createExporter().

onPrint() => void

Takes over the toolbar Print button and Ctrl / ⌘ + P; not called when the document forbids printing. When set, the SDK's Print dialog does not run; print with viewer.print({ pages }).

onSignatureRequest(field: FormFieldInfo | null) => Promise<{ dataUrl: string } | null>

Replaces the signature dialog, which then never opens. Called by the Sign tool (field is null) and by a form's signature field (field is that field); without the extract feature the field is blanked as formFieldChanged's is. Must resolve with { dataUrl } where dataUrl is a data: URL of a PNG, JPEG, WebP, GIF or BMP image, at most 10 MB. Anything else — null, a web address, SVG, a missing dataUrl — is a cancel, and so is a rejected promise (logged with console.warn). While a request is open, clicking the page or the same signature field again does not ask a second time. If the user switches tool before you answer, the answer is dropped.

onImageRequest() => Promise<Blob | null>

Replaces the Image tool's picker: called when the Image tool would open its file picker. Resolve with a Blob (a File is one) or null to cancel; the image is checked against tools.image like a picked file and refused with the same message. A rejection is a cancel and is logged; the SDK shows nothing for a cancel, so tell the user yourself if your flow failed. An answer that arrives after the tool was switched off is dropped.

onExternalLink(url: string) => void

Takes over web, mailto: and tel: links in the document. Receives only addresses that passed the SDK's scheme check: http:, https:, mailto: and tel: (an address written without a scheme arrives with https:// in front). javascript:, data: and every other scheme never reach it, in-document links still jump to their page, and links.confirmExternal no longer applies. The address is chosen by whoever wrote the document, so show it to the user before opening it, and open it with noopener,noreferrer. An exception thrown by your handler is logged with console.error.

onConfirm(request: ConfirmRequest) => Promise<boolean> | boolean

Replaces the confirmation dialog ("Delete this page?"). Called in place of the SDK's confirmation dialog, for every question confirmations has on, with the words the SDK would have shown (title, message, confirmLabel, cancelLabel) and what the action is about (action, count, name). name and message carry text from the document: show them as text, never HTML. Resolve true to go ahead; anything else, and a rejection (logged with console.warn), leaves things as they are.

onConfirmTypeScript

new PDFViewer(container, doc, {
  callbacks: {
    onConfirm: async ({ action, title, message, confirmLabel, cancelLabel, count, name }) =>
      myDialogs.confirm({ title, body: message, ok: confirmLabel, cancel: cancelLabel, tone: 'danger' }),
  },
});

Notes

Callbacks decide; events observe. A callback is where the SDK hands you a decision or a job of its own. Everything that merely happened is an event on viewer.on(...); the field snapshot formFieldChanged, formFieldFocused and formFieldBlurred carry is described under Events.

Ctrl / ⌘ + P goes to onPrint too. With the Print button hidden (toolbar.print: false), the key is left to the browser.

Callbacks

Example

Options 6

Notes

Related