JavaScript Events

HTML events are "things" that happen to HTML elements.

When JavaScript is used in HTML pages, JavaScript can "react" on these events.

HTML Events

An HTML event can be something the browser does, or something a user does.

Here are some examples of HTML events:

• An HTML web page has finished loading
• An HTML input field was changed
• An HTML button was clicked

Often, when events happen, you may want to do something.

JavaScript lets you execute code when events are detected.

HTML allows event handler attributes, with JavaScript code, to be added to HTML elements.

With single quotes:

With double quotes:

In the following example, an onclick attribute (with code), is added to a <button> element:

<button onclick="document.getElementById('demo').innerHTML = Date()">The time is?</button>

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):

<button onclick="this.innerHTML = Date()">The time is?</button>

<button onclick="displayDate()">The time is?</button>

Common HTML Events

Here is a list of some common HTML events:

These are some if the events only, this list is much longer.

JavaScript Event Handlers

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 ...