JavaScript Events

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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:


<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):

Example

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

Try it Yourself »


JavaScript code is often several lines long. It is more common to see event attributes calling functions:


Example

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


You will learn a lot more about events and event handlers in the HTML DOM chapters.



Test Yourself With Exercises

Exercise:
The <button> element should do something when someone clicks on it. Try to fix it!


<button ="alert('Hello')">Click me.</button>



Submit Answer »
Start the Exercise














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Reference: https://www.w3schools.com/js/js_events.asp