worker.ts

// @ts-ignore jsqr-es6 does not provide types currently
import jsQR from '../node_modules/jsqr-es6/dist/jsQR.js';

type GrayscaleWeights = {
    red: number,
    green: number,
    blue: number,
    useIntegerApproximation: boolean,
};

let inversionAttempts: 'dontInvert' | 'onlyInvert' | 'attemptBoth' = 'dontInvert';
let grayscaleWeights: GrayscaleWeights = {
    // weights for quick luma integer approximation (https://en.wikipedia.org/wiki/YUV#Full_swing_for_BT.601)
    red: 77,
    green: 150,
    blue: 29,
    useIntegerApproximation: true,
};

self.onmessage = event => {
    const id = event['data']['id'];
    const type = event['data']['type'];
    const data = event['data']['data'];

    switch (type) {
        case 'decode':
            decode(data, id);
            break;
        case 'grayscaleWeights':
            setGrayscaleWeights(data);
            break;
        case 'inversionMode':
            setInversionMode(data);
            break;
        case 'close':
            // close after earlier messages in the event loop finished processing
            self.close();
            break;
    }
};

function decode(data: { data: Uint8ClampedArray, width: number, height: number }, requestId: number): void {
    const rgbaData = data['data'];
    const width = data['width'];
    const height = data['height'];
    const result = jsQR(rgbaData, width, height, {
        inversionAttempts: inversionAttempts,
        greyScaleWeights: grayscaleWeights,
    });
    if (!result) {
        (self as unknown as Worker).postMessage({
            id: requestId,
            type: 'qrResult',
            data: null,
        });
        return;
    }

    (self as unknown as Worker).postMessage({
        id: requestId,
        type: 'qrResult',
        data: result.data,
        // equivalent to cornerPoints of native BarcodeDetector
        cornerPoints: [
            result.location.topLeftCorner,
            result.location.topRightCorner,
            result.location.bottomRightCorner,
            result.location.bottomLeftCorner,
        ],
    });
}

function setGrayscaleWeights(data: GrayscaleWeights) {
    // update grayscaleWeights in a closure compiler compatible fashion
    grayscaleWeights.red = data['red'];
    grayscaleWeights.green = data['green'];
    grayscaleWeights.blue = data['blue'];
    grayscaleWeights.useIntegerApproximation = data['useIntegerApproximation'];
}

function setInversionMode(inversionMode: 'original' | 'invert' | 'both') {
    switch (inversionMode) {
        case 'original':
            inversionAttempts = 'dontInvert';
            break;
        case 'invert':
            inversionAttempts = 'onlyInvert';
            break;
        case 'both':
            inversionAttempts = 'attemptBoth';
            break;
        default:
            throw new Error('Invalid inversion mode');
    }
}