Safe javascript decorator

decorate.js

/*
 Example of use
 document.write = decorate (document.write, function () {
	console.log(this === document);// true;
 }, function () {
	console.log('DOM is updated');
 });

 document.write = decorate (document.write, null, function () {
	console.log('After document.write');
 });
*/

function decorate (initial, decorate_before, decorate_after) {
	var name;

	function f () {
			var initial_call_result;

			try {
				if (typeof decorate_before === 'function') {
					decorate_before.apply(this, arguments);
				}
			} catch (err) {
				if (mmcore.EH) {
					mmcore.EH(err);
				}
			} finally {
				initial_call_result = initial.apply(this, arguments);
			}

			try {
				if (typeof decorate_after === 'function') {
					decorate_after.apply(this, arguments);
				}
			} catch (err) {
				if (mmcore.EH) {
					mmcore.EH(err);
				}
			} finally {
				return initial_call_result;
			}
		};

	// try to copy props from original function to decorated one
	// decorating may fail, if props are primitives
	for (name in initial[name]) {
		if (initial.hasOwnProperty(name)) {
			f[name] = initial[name];
		}
	}
	return f;
}

Update for cases, when function object carries properties