JavaScript
HTML DOM EventListener
The
addEventListener() method
Example
Add an event
listener that fires when a user clicks a button:
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").
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.
Note that
you don't use the "on" prefix for the event; use "click"
instead of "onclick".
Add an Event
Handler to an Element
Example
Alert
"Hello World!" when the user clicks on an element:
element.addEventListener("click",
function(){ alert("Hello World!"); });
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You can also
refer to an external "named" function:
Example
Alert
"Hello World!" when the user clicks on an element:
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
Add an event
listener that fires when a user resizes the window:
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 <p> element inside a <div> element, and the user clicks on
the <p> 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
<p> element's click event is handled first, then the <div>
element's click event.
In capturing
the outer most element's event is handled first and then the inner: the
<div> element's click event will be handled first, then the <p>
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);
»
Browser
Support
The numbers
in the table specifies the first browser version that fully supports these
methods.
Method
addEventListener() 1.0 9.0 1.0 1.0 7.0
removeEventListener() 1.0 9.0 1.0 1.0 7.0
Note: The
addEventListener() and removeEventListener() methods are not supported in IE 8
and earlier versions and Opera 6.0 and earlier versions. However, for these
specific browser versions, you can use the attachEvent() method to attach an
event handlers to the element, and the detachEvent() method to remove it:
element.attachEvent(event,
function);
element.detachEvent(event,
function);
Example
Cross-browser
solution:
var
x = document.getElementById("myBtn");
if
(x.addEventListener) { // For all major browsers, except IE 8
and earlier
x.addEventListener("click",
myFunction);
}
else if (x.attachEvent) {
// For IE 8 and earlier versions
x.attachEvent("onclick",
myFunction);
}
»
HTML DOM
Event Object Reference
For a list
of all HTML DOM events, look at our complete HTML DOM Event Object Reference.
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