To make it work you will need to handle the asynchronous nature of image loading. You will have to use a callback mechanism here. The reason it "works" in Chrome is accident; that is the image happen to be in the cache when you try and/or the browser is able to deliver the uncompressed/decoded image before you use the image in the drawImage call.
This will probably not work when it's online for most users so to properly handle loading you can do -
Example:
function getImageUri(url, callback) {
var image = new Image();
image.onload = function () { // handle onload
var image = this; // make sure we using valid image
var aspectRatio = getAspectRatio(parseFloat($(image).prop('naturalWidth')),
parseFloat($(image).prop('naturalHeight')),
dstWidth,
dstHeight);
var canvas = document.createElement('canvas');
canvas.width = dstWidth;
canvas.height = dstHeight;
var x = (dstWidth - aspectRatio[0]) / 2;
var y = (dstHeight - aspectRatio[1]) / 2;
var ctx = canvas.getContext("2d");
ctx.drawImage(image, x, y, aspectRatio[0], aspectRatio[1]);
// use callback to provide the finished data-uri
callback(canvas.toDataURL());
}
image.src = url; // set src last
}
Then use it this way:
getImageUri(myURL, function (uri) {
console.log(uri); // contains the image as data-uri
});