Detects whether an url is an image

is-image.js

function isImage (url, callback) {
	function cleanup () {
		delete img.onload;
		delete img.onerror;
		img = null;
	}

	var img = new Image();

	img.onload = function () {
		cleanup();
		callback(true);
	};

	img.onerror = function () {
		cleanup();
		callback(false);
	};

	img.src = url;
}