JavaScript Events
HTML Events
HTML events are things that happen to HTML elements.
Examples of events:
- An HTML button is clicked
- A web page has finished loading
- The mouse moves over an element
- A keyboard key is pressed
- An HTML input field is changed
JavaScript Events
Often, when events happen, you may want to do something.
When JavaScript is used in HTML pages, JavaScript can react on events.
JavaScript lets you execute code when events are detected.
HTML allows event handler attributes, with JavaScript code, to be added to HTML elements.
Syntax
With single quotes:
<element
event='some JavaScript'>
With double quotes:
<element
event="some JavaScript">
In the following example, an onclick attribute (with code), is added to a
<button> element:
Example
<button onclick="document.getElementById('demo').innerHTML = Date()">The time is?</button>
Try it Yourself »
In the example above, the JavaScript code changes the content of the element with id="demo".
In the next example, the code changes the content of
its own element using this.innerHTML:
Calling a JavaScript Function
JavaScript code can often be several lines long.
It is more common to use the event attribute to call a functions:
Example
<button onclick="displayDate()">The time is?</button>
<script>
function displayDate() {
document.getElementById("demo").innerHTML = Date();
}
</script>
Try it Yourself »
Common HTML Events
Here is a list of some common HTML events:
| Event | Description |
|---|---|
| onchange | An HTML element has been changed |
| onclick | The user clicks an HTML element |
| onmouseover | The user moves the mouse over an HTML element |
| onmouseout | The user moves the mouse away from an HTML element |
| onkeydown | The user pushes a keyboard key |
| onload | The browser has finished loading the page |
The list is much longer: W3Schools JavaScript Reference HTML DOM Events.
JavaScript Event Handlers
An event handler is JavaScript code that runs when an event happens.
Event handlers can be used to handle and verify user input, user actions, and browser actions:
- Things that should be done every time a page loads
- Things that should be done when the page is closed
- Action that should be performed when a user clicks a button
- Content that should be verified when a user inputs data
- And more ...
Many different methods can be used to let JavaScript work with events:
- HTML event attributes can execute JavaScript code directly
- HTML event attributes can call JavaScript functions
- You can assign your own event handler functions to HTML elements
- You can prevent events from being sent or being handled
- And more ...
Using an Event Listener
Using event attributes like onclick are easy to use.
Nevertheless, using addEventListener() is the recommended way to handle events.
Not Recommended
Using the onclick attribute:
<button onclick="displayDate()">Time is?</button>
<p id="demo"></p>
<script>
// Function to displat date
function displayDate() {
document.getElementById("demo").innerHTML = Date();
}
</script>
Try it Yourself »
The addEventListener() method keeps HTML and JavaScript separated.
Highly Recommended
Using addEventListener() method:
<button id="myBtn">Click me</button>
<p id="demo"></p>
<script>
const btn = document.getElementById("myBtn");
// Add EventListener to btn
btn.addEventListener("click", function () {
document.getElementById("demo").innerHTML = Date();
});
</script>
Try it Yourself »
Note
You will learn a lot more about events and event handlers in the HTML DOM chapters.
