> [!NOTE]
>
> For the v1 release, please visit the channel/v1 branch.

scanx-wasm

   

ZXing-C++ WebAssembly as an ES/CJS module with types. Read or write barcodes in various JS runtimes: Web, Node.js, Bun, and Deno.

Visit this online demo to quickly explore its basic reading functions. It works best on the latest Chromium browsers.

Build

``bash
git clone --recurse-submodules https://github.com/udvabok/scanx-wasm.git
cd scanx-wasm

Install pnpm before executing the next command:

pnpm build
`

Install

`bash
npm i scanx-wasm
`

Documentation

Demo

Demo page: https://scanx-wasm-demo.deno.dev/

Demo source: https://github.com/udvabok/scanx-wasm-demo

Usage

This package exports three subpaths: full, reader, and writer.

$3

These two subpaths provide functions to read and write barcodes. The wasm binary size is ~1.31 MB.

`ts
import { readBarcodes, writeBarcode } from "scanx-wasm";
`

or

`ts
import { readBarcodes, writeBarcode } from "scanx-wasm/full";
`

$3

This subpath only provides a function to read barcodes. The wasm binary size is ~911 KB.

`ts
import { readBarcodes } from "scanx-wasm/reader";
`

$3

This subpath only provides a function to write barcodes. The wasm binary size is ~600 KB.

`ts
import { writeBarcode } from "scanx-wasm/writer";
`

$3

Apart from ES and CJS modules, this package also ships IIFE scripts. The registered global variable is named ZXingWASM, where you can access all the exported functions and variables under it.

> [!NOTE]
> Replace the with the desired version number.

`html





`

$3

readBarcodes accepts an image Blob, image File, ArrayBuffer, Uint8Array, or an ImageData as its first argument, and various options are supported in ReaderOptions as an optional second argument.

The return result of this function is a Promise of an array of ReadResults.

e.g.

`ts
import { readBarcodes, type ReaderOptions } from "scanx-wasm/reader";

const readerOptions: ReaderOptions = {
tryHarder: true,
formats: ["QRCode"],
maxNumberOfSymbols: 1,
};

/**
* Read from image file/blob
*/
const imageFile = await fetch(
"https://api.qrserver.com/v1/create-qr-code/?size=150x150&data=Hello%20world!",
).then((resp) => resp.blob());

const imageFileReadResults = await readBarcodes(imageFile, readerOptions);

console.log(imageFileReadResults[0].text); // Hello world!

/**
* Read from image data
*/
const imageData = await createImageBitmap(imageFile).then((imageBitmap) => {
const { width, height } = imageBitmap;
const context = new OffscreenCanvas(width, height).getContext(
"2d",
) as OffscreenCanvasRenderingContext2D;
context.drawImage(imageBitmap, 0, 0, width, height);
return context.getImageData(0, 0, width, height);
});

const imageDataReadResults = await readBarcodes(imageData, readerOptions);

console.log(imageDataReadResults[0].text); // Hello world!
`

$3

The first argument of writeBarcode is a text string or an Uint8Array of bytes to be encoded, and the optional second argument WriterOptions accepts several writer options.

The return result of this function is a Promise of a WriteResult.

e.g.

`ts
import { writeBarcode, type WriterOptions } from "scanx-wasm/writer";

const writerOptions: WriterOptions = {
format: "QRCode",
scale: 3,
};

const writeOutput = await writeBarcode("Hello world!", writerOptions);

console.log(writeOutput.svg); // An SVG string.
console.log(writeOutput.utf8); // A multi-line string made up of " ", "▀", "▄", "█" characters.
console.log(writeOutput.image); // A PNG image blob.
`

Configuring .wasm Serving

$3

When using this package, a .wasm binary file needs to be served somewhere, so the runtime can fetch, compile and instantiate the WASM module. To provide a smooth development experience, the serve path is automatically assigned a jsDelivr CDN URL upon build.

If you want to change the serve path to your own server or other CDNs, please use prepareScanXModule and pass an overrides object with a custom defined locateFile function before reading or writing barcodes. locateFile is one of the Emscripten Module attribute hooks that can affect the code execution of the Module object during its lifecycle.

e.g.

`ts
import { prepareScanXModule, writeBarcode } from "scanx-wasm";

// Override the locateFile function
prepareScanXModule({
overrides: {
locateFile: (path, prefix) => {
if (path.endsWith(".wasm")) {
return https://unpkg.com/scanx-wasm@2/dist/full/${path};
}
return prefix + path;
},
},
});

// Call read or write functions afterward
const writeOutput = await writeBarcode("Hello world!");
`

> [!NOTE]
> An unexpected error occurred while initializing the module. Please ensure that a custom initialization function is provided, e.g.:
> The default jsDelivr CDN serve path is also achieved by overriding the custom locateFile function:
>
> `ts
> const DEFAULT_MODULE_OVERRIDES: ScanXModuleOverrides = {
> locateFile: (path, prefix) => {
> const match = path.match(/_(.+?)\.wasm$/);
> if (match) {
> return https://fastly.jsdelivr.net/npm/scanx-wasm@${SCANX_WASM_VERSION}/dist/${match[1]}/${path};
> }
> return prefix + path;
> },
> };
> `
>
> However, overrides is atomic. If you override other Module attributes, you _probably_ should also provide a locateFile function to ensure the .wasm file is fetched correctly.

$3

If you want to use this library in non-web runtimes (such as Node.js, Bun, Deno, etc.) without setting up a server, there are several possible approaches. Because API support can differ between runtime environments and versions, you may need to adapt these examples or choose alternative methods depending on your specific runtime’s capabilities. Below are some example configurations for Node.js.

1. Use the Module.instantiateWasm API

`ts
import { readFileSync } from "node:fs";
import { prepareScanXModule } from "scanx-wasm/reader";

const wasmFileBuffer = readFileSync("/path/to/the/scanx_reader.wasm");

prepareScanXModule({
overrides: {
instantiateWasm(imports, successCallback) {
WebAssembly.instantiate(wasmFileBuffer, imports).then(({ instance }) =>
successCallback(instance),
);
return {};
},
},
});
`

2. Use the Module.wasmBinary API

`ts
import { readFileSync } from "node:fs";
import { prepareScanXModule } from "scanx-wasm/reader";

prepareScanXModule({
overrides: {
wasmBinary: readFileSync("/path/to/the/scanx_reader.wasm")
.buffer as ArrayBuffer,
},
});
`

3. Use the Module.locateFile API with an Object URL

`ts
import { readFileSync } from "node:fs";
import { prepareScanXModule } from "scanx-wasm/reader";

// Create an Object URL for the .wasm file.
const wasmFileUrl = URL.createObjectURL(
new Blob([readFileSync("/path/to/the/scanx_reader.wasm")], {
type: "application/wasm",
}),
);

prepareScanXModule({
overrides: {
locateFile: (path, prefix) => {
if (path.endsWith(".wasm")) {
return wasmFileUrl;
}
return prefix + path;
},
// Call URL.revokeObjectURL(wasmFileUrl) after the ZXing module
// is fully instantiated to free up memory.
postRun: [
() => {
URL.revokeObjectURL(wasmFileUrl);
},
],
},
});
`

4. Use the Module.locateFile API with a Base64-encoded Data URL _(Not recommended)_

`ts
import { readFileSync } from "node:fs";
import { prepareScanXModule } from "scanx-wasm/reader";

const wasmBase64 = readFileSync("/path/to/the/scanx_reader.wasm").toString(
"base64",
);
const wasmUrl = data:application/wasm;base64,${wasmBase64};

prepareScanXModule({
overrides: {
locateFile: (path, prefix) => {
if (path.endsWith(".wasm")) {
return wasmUrl;
}
return prefix + path;
},
},
});
`

> [!NOTE]
> To use this library in a WeChat mini program , there are several things to keep in mind:
>
> 1. Only the scanx-wasm import path is supported; scanx-wasm/reader or scanx-wasm/writer is not supported.
> 2. Before using the library, you need to copy/move the node_modules/scanx-wasm/dist/full/scanx_full.wasm file into your project directory.
> 3. You must use prepareScanXModule to configure how the .wasm file will be fetched, loaded, and compiled before calling readBarcodes or writeBarcode. This is mandatory, and you can do so with the following code:
>
> `typescript
> prepareScanXModule({
> overrides: {
> instantiateWasm(imports, successCallback) {
> WXWebAssembly.instantiate("path/to/scanx_full.wasm", imports).then(
> ({ instance }) => successCallback(instance),
> );
> return {};
> },
> },
> });
> `
>
> Note that WeChat mini programs use WXWebAssembly instead of the standard WebAssembly, and the first argument in WXWebAssembly.instantiate should point to the location where the scanx_full.wasm file was moved earlier.
>
> 4. This library uses a bare minimum Blob polyfill in the mini program environment so that no errors will be thrown if you call writeBarcode. However, it's recommended to use a full-fledged Blob polyfill for not breaking other parts of your program.

> [!IMPORTANT]
>
> Each version of this library has a unique corresponding .wasm file. If you choose to serve it yourself, please ensure that the .wasm file matches the version of the scanx-wasm library you are using. Otherwise, you may encounter unexpected errors.

For convenience, this library provides an exported SCANX_WASM_VERSION variable to indicate the resolved version of the scanx-wasm you are using:

`ts
import { SCANX_WASM_VERSION } from "scanx-wasm";
`

The commit hash of the zxing-cpp submodule is exported as SCANX_CPP_COMMIT:

`ts
import { SCANX_CPP_COMMIT } from "scanx-wasm";
`

The SHA-256 hash of the .wasm file (in hex format) is also exported as SCANX_WASM_SHA256, in case you want to make sure you are serving the exactly same file:

`ts
import { SCANX_WASM_SHA256 } from "scanx-wasm";
`

To acquire the .wasm files for customized serving, in addition to finding them by searching in your node_modules folder, they can also be downloaded from CDNs like jsDelivr:

- scanx_full.wasm:

`text
https://cdn.jsdelivr.net/npm/scanx-wasm@/dist/full/scanx_full.wasm
`

- scanx_reader.wasm:

`text
https://cdn.jsdelivr.net/npm/scanx-wasm@/dist/reader/scanx_reader.wasm
`

- scanx_writer.wasm:

`text
https://cdn.jsdelivr.net/npm/scanx-wasm@/dist/writer/scanx_writer.wasm
`

Controlling .wasm Instantiation Timing and Caching

By default, the .wasm binary will not be fetched and instantiated until a readBarcodes or writeBarcode function is called. This behavior avoids unnecessary network requests and instantiation overhead if you decide to override the default .wasm serving path or other settings before using the library. Calling prepareScanXModule with overrides alone does not change this default behavior:

`ts
prepareScanXModule({
overrides: {
/ ... your desired overrides ... /
},
}); // <-- returns void
`

However, if you want to explicitly trigger the download and instantiation of the .wasm binary, you can set the fireImmediately option to true. Doing so also causes prepareScanXModule to return a Promise that resolves to the underlying Emscripten module. This allows you to await the instantiation process:

`ts
prepareScanXModule({
overrides: {
/ ... your desired overrides ... /
},
fireImmediately: true,
}); // <-- returns a promise
`

Because different overrides settings can influence how this library locates and instantiates the .wasm binary, the library performs an equality check on overrides to determine if the .wasm binary should be re-fetched and re-instantiated. By default, it is determined by a shallow comparison of the overrides object. If you prefer a different method of comparison, you can supply a custom equalityFn:

`ts
prepareScanXModule({
overrides: {
/ ... your desired overrides ... /
},
fireImmediately: true,
equalityFn: () => false, // <-- force re-fetch and re-instantiate
});
`

FAQ

1. Why are submodules required?

The core function of reading / writing barcodes of this library is provided by zxing-cpp. It is pinned to a specific commit ID as a submodule, and can be built as .wasm files. Additionally, the barcode generation ability is provided by zint, which is a submodule inside zxing-cpp, so it is necessary to clone the repository with --recurse-submodules to ensure that all required submodules are also cloned.

2. I forgot to clone the repository with --recurse-submodules, how should I install the submodules without deleting this repo and cloning it again?

In the root of the repo, run:

`bash
git submodule update --init --recursive
`

3. Are there any higher level libraries that can be used to simplify the usage of this library?
- barcode-detector: A Barcode Detection API polyfill / ponyfill that uses this library under the hood.
- vue-qrcode-reader: A set of Vue.js components for detecting QR codes and various other barcode formats right in the browser which uses barcode-detector under the hood.
- @yudiel/react-qr-scanner: A library to scan QR Codes in react which uses barcode-detector under the hood.
- svelte-qrcode-reader: A set of Svelte 5 components for detecting and decoding QR-codes which uses barcode-detector under the hood.

A React toolkit for scanning barcodes directly based on this library is planned, which aims to provide easy-to-use capabilities for interacting with web cameras.

4. One of the input types of readBarcodes is ImageData, which is a DOM type. How can I use it in Node.js or other runtimes?

The types are duck-typed, so you can use it in Node.js or other runtimes by providing a DOM-compatible ImageData object in the following shape, where the image data should be in RGBA format:

`ts
interface ImageData {
data: Uint8ClampedArray;
width: number;
height: number;
}
``

Licenses

This project contains code from multiple sources, each with its own license:

- zxing-cpp: Apache License 2.0
- src/cpp/ScanXWasm.cpp: Apache License 2.0
- zint: BSD 3-Clause License
- scanx-wasm specific code: MIT License