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You can use browser APIs to turn an already-valid PDF byte sequence into a preview or download without installing a package. Those APIs do not create the PDF’s internal structure: a hand-built writer must produce correct PDF bytes first, and that work includes formatting and compatibility details.
What “zero-dependency” means in a browser
Blob, URL.createObjectURL(), and an anchor’s download attribute are browser platform features, not third-party packages. They handle delivery of PDF bytes, but they are not a PDF generator by themselves.
The distinction matters: the code below assumes pdfBytes is already a valid PDF byte sequence. It does not build a PDF from text, define PDF objects, or guarantee that arbitrary bytes will open correctly.
Preview or download an existing PDF byte sequence
Once your code has valid PDF bytes, create a PDF Blob and choose whether to show it in an iframe or offer a download link:
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const blob = new Blob([pdfBytes], { type: 'application/pdf' });
const url = URL.createObjectURL(blob);
// Preview it:
iframe.src = url;
// Or offer a download:
link.href = url;
link.download = 'document.pdf';The anchor’s download value suggests a filename; it does not guarantee a silent save. Browser settings, prompts, and implementation can affect what happens. MDN documents both the object URL API and download attribute.
Release the object URL at the right time
An object URL keeps its underlying Blob available while the URL is active. Release it with URL.revokeObjectURL(url) once the user no longer needs to use the preview or download resource. Revoking immediately after assigning an iframe source can make the resource unavailable before the user has finished with it.
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// When replacing or removing the preview:
URL.revokeObjectURL(url);MDN explains the revocation lifecycle. The right cleanup moment depends on your interface: keep the URL while the preview is in use, then revoke it when replacing or removing that preview.
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Choose how to create the PDF bytes
The main engineering decision is not how to download the file; it is whether to maintain a PDF writer yourself or use a library whose feature set and browser behavior match the job.
| Approach | What it provides | Costs and constraints |
|---|---|---|
| Hand-built vanilla JavaScript | No third-party package dependency; full control over the code you write. | You own PDF formatting and compatibility. The browser delivery APIs do not solve PDF structure, text encoding, fonts, or other format requirements. |
| pdf-lib | Project documentation describes browser support and creation and modification of PDFs, including pages, text, images, custom fonts, forms, and merge/split operations. save() returns a Uint8Array that can be passed to the Blob flow. |
It is a third-party dependency. Embedding custom fonts requires the separate @pdf-lib/fontkit module. |
| PDFKit | Supports browser use; its documented browser pattern collects document chunks into an application/pdf Blob, then creates an object URL for preview. |
The browser build cannot access the filesystem, and standard fonts need registration in the browser build. Its toBlob and toBytes output helpers are documented as experimental. |
For pdf-lib’s documented capabilities and browser output, see the pdf-lib project documentation. For PDFKit’s browser usage and browserify output example, consult its project documentation. PDFKit’s example demonstrates collecting chunks before constructing the Blob rather than treating the Blob step as PDF generation.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When a hand-built writer is a reasonable choice
A custom writer can make sense when the output is tightly controlled, the document needs are deliberately small, and you are prepared to own format correctness and browser compatibility. It is a poor shortcut if the requirement quietly expands to arbitrary text, embedded fonts, images, forms, edits to existing files, or reliable interchange across viewers.
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- Define the exact documents and features you need before choosing the approach.
- Account for the maintenance burden of producing valid PDF structure, not just a downloadable file.
- Choose a library when its documented features reduce the amount of PDF-format behavior your application must implement and maintain.
The browser output flow is the easy final step. A Blob can package bytes, but it cannot make invalid or incomplete PDF bytes valid.
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