stopPropagation is used to make sure the event doesn't bubble up the chain. eg. a click on a <td> tag would also fire click events on it's parent <tr>, and then its parent <table>, etc. stopPropagation prevents this from happening. preventDefault is used to stop the normal action of an element, eg. preventDefault in a click handler on a link would stop the link being followed, or on a submit button would stop the form being submitted.