sinon.spy wrapper for IE8

spyOn.js

/**
 * Spy on an object in a way that IE8 likes it
 *
 * If trying to use sinon.spy(document, 'createElement') or such in IE8,
 * it will not work correctly. This function wraps the call in a way
 * that it's supported in IE.
 *
 * May have possible side-effects to more specialized asserts,, but
 * at least calledWith, return values, etc.  * work correctly.
 *
 * @param {object} obj
 * @param {string} method
 * @return {spy}
 */
function spyOn(obj, method) {
	var actual = obj[method];

	var spy = sinon.spy(function() { return actual.apply(obj, arguments); });

	spy.restore = function() {
		obj[method] = actual;
	};

	obj[method] = spy;

	return spy;
}