It's more useful to split them up like this (copy pasted some old code I wrote that works across browsers):
```
	function preventDefault(event) {
		if (event.preventDefault) {
			event.preventDefault();
		} else {
			event['returnValue'] = false;
		}
	}

	function stopPropagation(event) {
		if (event.stopPropagation) {
			event.stopPropagation();
		} else {
			event['cancelBubble'] = true;
		}
	}
```