canvas.toBlob does not exist on edge.

[Losses]

On edge, canvas.toBlob does not exist, but there's a similar (but not same) method named canvas.msToBlob.

To erase the error, I wrote some dirty workaround:

HTMLCanvasElement.prototype.toBlob = function(callback) {
  callback(this.msToBlob());
}

but it's not a good solution, maybe we need a better way to deal with it?