Stops the event’s propagation and prevents its default action from being triggered eventually.

There are two aspects to how your browser handles an event once it fires up:

Because stopping one of those aspects means, in 99.9% of the cases, preventing the other one as well, Prototype bundles both in this stop function. Calling it on an event object stop propagation and prevents the default behavior.


Here’s a simple code that prevents a form from being sent to the server side if a certain field is empty.

Event.observe('signinForm', 'submit', function(event) {
  var login = $F('login').strip();
  if ('' == login) {
    // Display the issue one way or another