Get image data (pixel RGB array, width, height) by URL

getImageData.js

// Only works for images hosted on the same domain unless CORs headers of image allow you to use it.
// Usage:
//   let data = await getImageData("http://example.com/image.png");
// Put it in a try/catch to handle errors or use await getImageData("...").catch(e => ...);
function getImageData(url) {
  return new Promise((resolve, reject) => {
    let img = new Image();
    img.onload = function() {
      let canvas = document.createElement("canvas");
      canvas.width = img.width;
      canvas.height = img.height;
      let ctx = canvas.getContext("2d");
      ctx.drawImage(img, 0, 0, canvas.width, canvas.height);
      resolve( ctx.getImageData(0, 0, canvas.width, canvas.height) );
    };
    img.onerror = reject;
    img.src = url;
  });
}