The script works but need some fixes:

• Change the detection of the path "/draw" for a regular expression (line 39):

const pattern = /\/([a-zA-Z]*)\/draw/g;
if (location.pathname.match(pattern)) {
// code...
}

• Handle centering and aspect ratio by changing the onload function (line 93):

img.onload = function() {
var x, y = 0;
var wRatio, hRatio = 0;
var width = canvas.width;
var height = canvas.height;
//Aspect ratio
if (img.width > canvas.width || img.height > canvas.height) {
wRatio = img.width / canvas.width;
hRatio = img.height / canvas.height;
if (wRatio > hRatio) {
width = canvas.width;
height = img.height / wRatio;
} else {
height = canvas.height;
width = img.width / hRatio;
}
} else {
width = img.width;
height = img.height;
}
//Center
x = (canvas.width - width) / 2;
y = (canvas.height - height) / 2;
//Draw
context.drawImage(this, x, y, width, height);
}