captureImage.js

function captureImage() {
  const { decode_qr } = wasm_bindgen;
  const video = document.getElementById('video');
  const canvas = document.createElement('canvas');
  const scale = 0.25; // we scale the image down to improve performance

  canvas.width = video.videoWidth * scale;
  canvas.height = video.videoHeight * scale;
  canvas
    .getContext("2d")
    .drawImage(video, 0, 0, canvas.width, canvas.height);

  canvas.toBlob(blob => {
    const reader = new FileReader();

    reader.addEventListener("loadend", () => {
      const arrayBuffer = reader.result;

      const output = decode_qr(new Uint8Array(arrayBuffer));

      console.log("output of decode_qr:", output);
    });
    reader.readAsArrayBuffer(blob);
  });
};