JavaScript Events


HTML events are things that happen to HTML elements.

When JavaScript is used in HTML pages, JavaScript can trigger these events.


HTML Events

HTML events can be browser behaviors or user behaviors.

The following are examples of HTML events:

  • HTML page finished loading

  • When the HTML input field changes

  • HTML button is clicked

Usually, when an incident occurs, you can do something.

JavaScript can execute some code when the event is triggered.

You can add event attributes to HTML elements, and use JavaScript code to add HTML elements.

apostrophe:

<some-HTML-element some-event = 'JavaScript code'>

Double quotes:

<some-HTML-element some-event = "JavaScript codes">

In the following example, the onclick attribute (plus code) is added to the button element:

Example

<button onclick="getElementById('demo').innerHTML=Date()">What is the time now?</button>

 Try It! 

In the above example, the JavaScript code will modify the content of the id="demo" element.

In the next example, the code will modify the content of its own element (using this .innerHTML):

Example

<button onclick="this.innerHTML=Date()">What is the time now?</button>
NoteJavaScript code is usually a few lines of code. It is more common to call through the event properties:

Try It! 

Example

<button onclick="displayDate()">What is the time now?</button>

 Try It! 


Common HTML Events

Below is a list of some common HTML events:

EventDescription
onchangeHTML element changes
onclickUser clicks on HTML element
onmouseoverThe user moves the mouse on an HTML element
onmouseoutThe user removes the mouse from an HTML element
onkeydownThe user presses a keyboard key
onloadThe browser has finished loading the page

More event list: JavaScript Reference Manual - HTML DOM Events .


What Can JavaScript Do?

Events can be used to handle form validation, user input, user behavior and browser actions:

  • Trigger an event when the page loads

  • Event triggered when the page is closed

  • The user clicks a button to perform an action

  • Verify the legitimacy of user input

  • and many more...

There are several ways to execute JavaScript event code:

  • HTML event attributes can directly execute JavaScript code

  • HTML event attributes can call JavaScript functions

  • You can specify your own event handlers for HTML elements

  • You can prevent the incident from happening.

  • and many more...

NoteIn the HTML DOM chapter you will learn more about events and event handlers.