qrcode

qrcode is an npm library for generating QR codes and 2D barcodes from server-side Node.js code or directly in the browser. It builds the QR symbol from scratch (segment optimization, Reed-Solomon error correction, mask-pattern selection) and ships pluggable renderers that can output the result as a PNG file or buffer, an SVG string, a data URL, raw terminal text, or directly onto an HTML5 canvas element.

Both a callback-based and a Promise/async-await API are supported for every render target, and the package also installs a qrcode CLI binary so a QR code can be generated or previewed from a shell one-liner without writing any code.

What You Get

• A spec-compliant QR Code encoder supporting Numeric, Alphanumeric, Kanji, and Byte modes with automatic mixed-mode segmentation for the smallest possible symbol
• Renderers for canvas, PNG (file, buffer, or data URL), SVG, UTF-8/terminal text, and writable file streams
• A dual callback/Promise API across every render function (toDataURL, toBuffer, toFile, toFileStream, toString, toCanvas)
• A globally installable qrcode CLI for generating QR images or previewing them directly in the terminal
• Configurable error correction levels (L/M/Q/H), symbol version, mask pattern, quiet zone, and custom foreground/background colors

Common Use Cases

• Generating login/2FA QR codes (e.g. TOTP otpauth:// URIs) for authenticator app enrollment
• Rendering shareable QR codes for URLs, contact cards, or Wi-Fi credentials on server-rendered pages or PDFs
• Embedding scannable payment or ticket codes in receipts and event passes generated as PNG/SVG assets
• Client-side QR generation directly onto a <canvas> element for real-time previews as a user types

Under The Hood

Architecture — The encoder lives entirely under lib/core/ as a pipeline of small, single-purpose modules: segments.js splits input into Numeric/Alphanumeric/Kanji/Byte runs, version.js picks the smallest QR version that fits, bit-buffer.js and reed-solomon-encoder.js/polynomial.js/galois-field.js build and error-correct the codeword stream, and qrcode.js (createSymbol) assembles the final BitMatrix by laying down finder, timing, alignment, and format-info patterns before mask-pattern.js scores all eight masks and applies the best one. lib/index.js (Node) and lib/browser.js (browser) are thin adapters that call QRCode.create() and hand the resulting matrix to one of five interchangeable renderers under lib/renderer/ (canvas, png, svg, terminal, utf8), so the same core encoder drives every output format.

Tech Stack — Runtime dependencies are minimal and purpose-built: pngjs for PNG encoding, dijkstrajs for shortest-path segment-mode optimization, and yargs for the CLI’s argument parsing. The browser bundle is produced via Rollup with Babel’s preset-env, and standard enforces lint rules as a pretest hook, so a broken style fails CI before tests even run.

Code Quality — Test coverage is thorough and organized to mirror the source layout: 26 unit test files under test/unit/core and test/unit/renderer exercise each internal module in isolation (bit-buffer, mask-pattern, reed-solomon-encoder, etc.), while test/e2e/*.test.js drives the public toCanvas/toDataURL/toFile/toFileStream/toString API end-to-end using tap and sinon. Functions are short, consistently documented with JSDoc blocks, and side effects (like the mutable toSJISFunc set on Utils) are the rare exception rather than the norm.

API Design — The public surface is deliberately small and uniform: every to* render function accepts the same (data, options, callback) shape and transparently returns a Promise when the callback is omitted, so consumers opt into whichever async style fits their codebase without adapter code. Getting a QR code onto the screen or into a file takes one line (QRCode.toDataURL(text, cb)), and the same mental model extends to the CLI binary, keeping the learning curve low for a spec-heavy domain.