JavaScript EventListener

The addEventListener() method

Example

document.getElementById("myBtn").addEventListener("click", displayDate);

The addEventListener() method attaches an event handler to the specified element.

The addEventListener() method attaches an event handler to an element without overwriting existing event handlers.

You can add many event handlers to one element.

You can add many event handlers of the same type to one element, i.e two "click" events.

You can add event listeners to any DOM object not only HTML elements. i.e the window object.

The addEventListener() method makes it easier to control how the event reacts to bubbling.

When using the addEventListener() method, the JavaScript is separated from the HTML markup, for better readability and allows you to add event listeners even when you do not control the HTML markup.

You can easily remove an event listener by using the removeEventListener() method.

Syntax

element.addEventListener(event, function, useCapture);

The first parameter is the type of the event (like "click" or "mousedown" or any other HTML DOM Event.)

The second parameter is the function we want to call when the event occurs.

The third parameter is a boolean value specifying whether to use event bubbling or event capturing. This parameter is optional.

Add an Event Handler to an Element

Example

element.addEventListener("click", function(){ alert("Hello World!"); });

You can also refer to an external "named" function:

Example

element.addEventListener("click",  myFunction);

function myFunction() {
  alert ("Hello World!");
}

Add Many Event Handlers to the Same Element

The addEventListener() method allows you to add many events to the same element, without overwriting existing events:

Example

element.addEventListener("click", myFunction);

 element.addEventListener("click", mySecondFunction);

You can add events of different types to the same element:

Example

element.addEventListener("mouseover", myFunction);

element.addEventListener("click", mySecondFunction);

element.addEventListener("mouseout", myThirdFunction);

Add an Event Handler to the window Object

The addEventListener() method allows you to add event listeners on any HTML DOM object such as HTML elements, the HTML document, the window object, or other objects that support events, like the xmlHttpRequest object.

Example

window.addEventListener("resize", function(){

  document.getElementById("demo").innerHTML = sometext;

});

Passing Parameters

When passing parameter values, use an "anonymous function" that calls the specified function with the parameters:

Example

element.addEventListener("click", function(){ myFunction(p1, p2); });

Event Bubbling or Event Capturing?

There are two ways of event propagation in the HTML DOM, bubbling and capturing.

Event propagation is a way of defining the element order when an event occurs. If you have a element inside a element, and the user clicks on the element, which element's "click" event should be handled first?

In bubbling the inner most element's event is handled first and then the outer: the element's click event is handled first, then the element's click event.

In capturing the outer most element's event is handled first and then the inner: the element's click event will be handled first, then the element's click event.

With the addEventListener() method you can specify the propagation type by using the "useCapture" parameter:

addEventListener(event, function, useCapture );

The default value is false, which will use the bubbling propagation, when the value is set to true, the event uses the capturing propagation.

Example

document.getElementById("myP").addEventListener("click", myFunction, true);

document.getElementById("myDiv").addEventListener("click", myFunction, true);

The removeEventListener() method

The removeEventListener() method removes event handlers that have been attached with the addEventListener() method:

Example

element.removeEventListener("mousemove", myFunction);

HTML DOM Event Object Reference

For a list of all HTML DOM events, look at our complete HTML DOM Event Object Reference.