JavaScript Events

The change in the state of an object is known as an Event. In html, there are various events which represents that some activity is performed by the user or by the browser. When javascript code is included in HTML, js react over these events and allow the execution. This process of reacting over the events is called Event Handling. Thus, js handles the HTML events via Event Handlers.

For example, when a user clicks over the browser, add js code, which will execute the task to be performed on the event.

Event Handler Uses:

It can be used directly within HTML elements by adding special attributes to those elements. They can also be used within the <script> tags or in external JavaScript files.

Some of the HTML events and their event handlers are:

Mouse events:

Event Performed	Event Handler	Description
click	onclick	When mouse click on an element
mouseover	onmouseover	When the cursor of the mouse comes over the element
mouseout	onmouseout	When the cursor of the mouse leaves an element
mousedown	onmousedown	When the mouse button is pressed over the element
mouseup	onmouseup	When the mouse button is released over the element
mousemove	onmousemove	When the mouse movement takes place.

Keyboard events:

Event Performed	Event Handler	Description
Keydown & Keyup	onkeydown & onkeyup	When the user press and then release the key

Form events:

Event Performed	Event Handler	Description
focus	onfocus	When the user focuses on an element
submit	onsubmit	When the user submits the form
blur	onblur	When the focus is away from a form element
change	onchange	When the user modifies or changes the value of a form element

Window/Document events

Event Performed	Event Handler	Description
load	onload	When the browser finishes the loading of the page
unload	onunload	When the visitor leaves the current webpage, the browser unloads it
resize	onresize	When the visitor resizes the window of the browser
reset	onreset	When the window size is resized
scroll	onscroll	When the visitor scrolls a scrollable area

Let's discuss some examples over events and their handlers.

Click Event

<html>
<head> Javascript Events </head>
<body>
<script language="Javascript" type="text/Javascript">
	<!--
	function clickevent()
	{
		document.write("This is JavaTpoint");
	}
	//-->
</script>
<form>
<input type="button" onclick="clickevent()" value="Who's this?"/>
</form>
</body>
</html>

Test it Now

Explanation:

In the above given example, we have created a function "clickevent" which is called by using the "onclick" event. When a user will click on this button then this function will be called, function will return a string "This is JavaTpoint" and "document.write" function will help to write the returned string on the document.

MouseOver Event

<html>
<head> 
<h1> Javascript Events </h1>
</head>
<body>
<script language="Javascript" type="text/Javascript">
	<!--
	function mouseoverevent()
	{
		alert("This is JavaTpoint");
	}
	//-->
</script>
<p onmouseover="mouseoverevent()"> Keep cursor over me</p>
</body>
</html>

Test it Now

Explanation:

In the above given example, we have created a function "mouseoverevent" which is called by using the "onmouseover" event. When a user will mouser over a <p> text then this function will be called and an alert box will be displayed. We can reuse the mouseoverevent function as many as need in our program, so it will save memory.

Focus Event

<html>
<head> Javascript Events</head>
<body>
<h2> Enter something here</h2>
<input type="text" id="input1" onfocus="focusevent()"/>
<script>
<!--
	function focusevent()
	{
		document.getElementById("input1").style.background=" aqua";
	}
//-->
</script>
</body>
</html>

Test it Now

Explanation:

In the above given example, we have created a function "focusevent" which is called by using the "onfocus" event. When a user will focus on a text field then this function will be called and a text field background color will be changed.

Keydown Event

<html>
<head> Javascript Events</head>
<body>
<h2> Enter something here</h2>
<input type="text" id="input1" onkeydown="keydownevent()"/>
<script>
<!--
	function keydownevent()
	{
		document.getElementById("input1");
		alert("Pressed a key");
	}
//-->
</script>
</body>
</html>

Test it Now

Explanation:

In the above given example, we have created a function "keydownevent" which is called by using the "onkeydown" event. When a user will focus on a text field then this function will be called and a alert box will be displayed.

Load event

<html>
<head>Javascript Events</head>
</br>
<body onload="window.alert('Page successfully loaded');">
<script>
<!--
document.write("The page is loaded successfully");
//-->
</script>
</body>
</html>

Test it Now

Explanation:

In the above example, we created an "onload" event on the html's <body> tag. When a HTML body will be loaded then a function will return a string "The page is loaded successfully" and "document.write" function will help to write the returned string on the document.

Next TopicJavaScript addEventListener()

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