How to use Node.js to determine whether a png image has transparent pixels

import canvas from 'canvas';
import fs from 'fs';

/**
 * Determine whether there are transparent pixels in the png image*
 * @param {*} pngPath png image path * @param {number} [limit=255] transparent pixel limit, by default less than 255 is considered transparent pixels * @param {boolean} [isToJpg=false] if there is no transparent pixel, whether to convert to jpg image * @returns
 */
function hasOpacity(pngPath, limit = 255, isToJpg = false) {
  // Get the image buffer
  const buffer = fs.readFileSync(pngPath);

  // The width of the image is stored in the 17th to 20th bytes of the buffer const width = buffer.readUInt32BE(16);
  // The width of the image is stored in the 21st to 24th bytes of the buffer const height = buffer.readUInt32BE(20);

  // Create a canvas const pngCanvas = canvas.createCanvas(width, height);
  // Get the brush const context = pngCanvas.getContext('2d');
  // Create an image const img = new canvas.Image();
  // Record the image img.src = buffer;
  // Use the brush to draw the picture on the canvas context.drawImage(img, 0, 0, width, height);

  // Get the pixel data of the png image let res = context.getImageData(0, 0, width, height);
  let imgData = res.data;
  // Each pixel takes up 4 bytes, calculate how many pixels there are in total // [r, g, b, a]
  let piexCount = imgData.length / 4;

  // Have transparent pixels been found? let isOpacity = false;

  for (let i = 0; i < piexCount; i++) {
    // Traverse each pixel and find the transparent channel let opacity = imgData[i * 4 + 3];
    if (opacity < limit) {
        // If it is less than limit, there are transparent pixels and exit isOpacity = true;
      break;
    }
  }

  // If there are no transparent pixels and isToJpg is true, convert the image to jpg format if (!isOpacity && isToJpg) {
    const out = fs.createWriteStream(pngPath.split('.')[0] + '.jpg');
    pngCanvas.createJPEGStream().pipe(out);
    out.on('finish', () => console.log(pngPath, 'Converted to jpg successfully'));
  }

  // return return isOpacity;
}

console.log(hasOpacity('hh.png', 254, true));
console.log(hasOpacity('jj.png'));