Extract layers from PDF in Node.js

async function main() {
    const doc = await PDFNet.PDFDoc.createFromURL(filename);
    const page = await doc.getPage(1);

    const initCfg = await doc.getOCGConfig();
    const ctx = await PDFNet.OCGContext.createFromConfig(initCfg);

    const pdfdraw = await PDFNet.PDFDraw.create();
    pdfdraw.setImageSize(1000, 1000);
    pdfdraw.setOCGContext(ctx);

    // Disable drawing of content that is not optional (i.e. is not part of any layer).
    ctx.setNonOCDrawing(false);

    // Now render each layer in the input document to a separate image.
    const ocgs = await doc.getOCGs(); // Get the array of all OCGs in the document.
    let i;
    const sz = await ocgs.size();
    for (i = 0; i < sz; ++i) {
        const ocg = await PDFNet.OCG.createFromObj(await ocgs.getAt(i));
        ctx.resetStates(false);
        ctx.setState(ocg, true);
        let fname = 'pdf_layers_';
        fname += await ocg.getName();
        fname += '.png';
        const pageBuffer = await pdfdraw.exportStream(page);
        const imageData = new Blob([pageBuffer], {type: 'image/png'}));
    }

    // Now draw content that is not part of any layer...
    ctx.setNonOCDrawing(true);
    ctx.setOCDrawMode(PDFNet.OCGContext.OCDrawMode.e_NoOC);
    const nonLayerBuffer = await pdfdraw.exportStream(page);
    const data = new Blob([nonLayerBuffer], {type: 'image/png'}));
}
PDFNet.runWithCleanup(main);