Prototype Event observe() Method


This method registers an event handler on a DOM element.

To register a function as an event handler, the DOM element that you want to observe must already exist in the DOM.



Here are the explanations about the passed parameters:

  • element: The DOM element you want to observe; as always in Prototype, this can be either an actual DOM reference, or the ID string for the element.

  • evenetName: The standardized event name, as per the DOM level supported by your browser. This includes click, mousedown, mouseup, mouseover, mousemove and mouseout.

  • handler: This is the event handler function. This can be an anonymous function you create on-the-fly.

  • useCapture: Optionally, you can request capturing instead of bubbling. The details are in the DOM Level 2 Events

Return Value

  • NA.


Here is an example, which observe click event and take an action whenever a click event occurs.

<title>Prototype examples</title>
   <script type="text/javascript" 


// Register event 'click' and associated call back.
Event.observe(document, 'click', respondToClick);
// Callback function to handle the event.
function respondToClick(event) {
  alert("You pressed the button...." );



   <p id="note"> Click anywhere to see the result.</p>

   <p id="para1">This is paragraph 1</p>
   <p id="para2">This is paragraph 2</p>

   <div id="division">
       This is divsion.


To understand it in better way you can Try it yourself.