Download external image on button click

index.js

function downloadImage(data, filename = 'untitled.jpeg') {
    var a = document.createElement('a');
    a.href = data;
    a.download = filename;
    document.body.appendChild(a);
    a.click();
}

document.getElementById('btn-download').addEventListener("click", function(e) {
    const canvas = document.createElement('canvas');
    const ctx = canvas.getContext('2d');
    const img = new Image();
    img.crossOrigin = '';
    img.src = "https://robohash.org/robert"
    img.onload = function() {
      const img = this;
      canvas.width = img.width;
      canvas.height = img.height;
      ctx.drawImage(img, 0, 0, img.width, img.height);
      
      const dataURL = canvas.toDataURL();
      
      downloadImage(dataURL, 'my-canvas.jpeg');
    }
});