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14.9 JS DOM Events

HTML DOM allows JavaScript to react to HTML events:

Reacting to Events

A JavaScript can be executed when an event occurs, like when a user clicks on an HTML element.
To execute code when a user clicks on an element, add JavaScript code to an HTML event attribute:

onclick=JavaScript

Examples of HTML events:
- When a user clicks the mouse
- When a web page has loaded
- When an image has been loaded
- When the mouse moves over an element
- When an input field is changed
- When an HTML form is submitted
- When a user strokes a key
In this example, the content of the <h1> element is changed when a user clicks on it:

Example 1: JS HTML Events - The onclick Attribute part 1

<!DOCTYPE html>
<html>
<body>

<h1 onclick="this.innerHTML = 'Ooops!'">Click on this text!</h1>

</body>
</html>

In this example, a function is called from the event handler:

Example 2: JS HTML Events - The onclick Attribute part 2

<!DOCTYPE html>
<html>
<body>

<h1 onclick="changeText(this)">Click on this text!</h1>

<script>
function changeText(id) {
  id.innerHTML = "Ooops!";
}
</script>

</body>
</html>

HTML Event Attributes

To assign events to HTML elements you can use event attributes.

Example 3: JS HTML Events - The onclick Attribute part 3

Assign an onclick event to a button element:

<button onclick="displayDate()">Try it</button>

In the example above, a function named displayDate will be executed when the button is clicked.

Assign Events Using the HTML DOM

The HTML DOM allows you to assign events to HTML elements using JavaScript:

Example 4: JS HTML Events - The onclick Attribute part 4

Assign an onclick event to a button element:

<script>
document.getElementById("myBtn").onclick = displayDate;
</script>

The onload and onunload Events

The onload and onunload events are triggered when the user enters or leaves the page.
The onload event can be used to check the visitor's browser type and browser version, and load the proper version of the web page based on the information.
The onload and onunload events can be used to deal with cookies.

Example 5: JS HTML Events - The onload Attribute

<body onload="checkCookies()">

The onmouseover and onmouseout Events

The onmouseover and onmouseout events can be used to trigger a function when the user mouses over, or out of, an HTML element:

Try ityourself

The onmousedown, onmouseup and onclick Events

The onmousedown, onmouseup and onclick events are all parts of a mouse-click. First when a mouse-button is clicked, the onmousedown event is triggered, then, when the mouse-button is released, the onmouseup event is triggered, finally, when the mouse-click is completed, the onclick event is triggered.

Try it yourself

More Examples

onmousedown and onmouseup: Change an image when a user holds down the mouse button.
onload: Display an alert box when the page has finished loading.
onfocus: Change the background-color of an input field when it gets focus.
Mouse Events: Change the color of an element when the cursor moves over it.

HTML DOM Event Object Reference

For a list of all HTML DOM events, look at the complete HTML DOM Event Object Reference.

JavaScript Fundamentals course home
Module 14. JS HTML DOM

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Example files created in this module:
HTML DOM Methods JS HTML DOM - Finding HTML Element by Id JS HTML DOM - Finding HTML Elements by Tag Name part 1 JS HTML DOM - Finding HTML Elements by Tag Name part 2 JS HTML DOM - Finding HTML Elements by Class Name JS HTML DOM - Finding HTML Elements by CSS Selectors JS HTML DOM - Finding HTML Elements by HTML document.forms JS Changing HTML Content part 1 JS Changing HTML Content part 2 JS HTML DOM - Changing the Value of an Attribute JS HTML DOM - Dynamic HTML content JS HTML DOM - document.write() JS Validation - HTML Form Example part 1 JS Validation - HTML Form Example part 2 JS HTML DOM - Changing the HTML style JS HTML DOM - Changing the HTML style Using Events My first JS animation part 1 My first JS animation part 2 JS HTML Events - The onclick Attribute part 1 JS HTML Events - The onclick Attribute part 2 JS HTML Events - The onclick Attribute part 3 JS HTML Events - The onclick Attribute part 4 JS HTML Events - The onload Attribute JS addEventListener() part 1 JS addEventListener() part 2 JS addEventListener() part 3 JS addEventListener() part 4 JS addEventListener() part 5 JS addEventListener() part 6 JS addEventListener() part 7 JS addEventListener() part 8 JS removeEventListener() JS HTML Child Nodes and Node Values part 1 JS HTML Child Nodes and Node Values part 2 JS HTML Child Nodes and Node Values part 3 JS HTMLDOM - DOM Root Nodes part 1 JS HTMLDOM - DOM Root Nodes part 2 JS HTMLDOM - The nodeName Property JS HTMLDOM - The nodeType Property JS HTML DOM - Creating New HTML Elements (Nodes) JS HTML DOM - Creating new HTML Elements - insertBefore() JS HTML DOM - Removing Existing HTML Elements JS HTML DOM - Remove Child Element JS HTML DOM - Replacing an HTML Elements JS HTML DOM Collections JS HTML DOM Collections - HTMLCollection Length par 1 JS HTML DOM Collections - HTMLCollection Length part 2 JS HTML DOM - DOM Node Lists JS HTML DOM - DOM Node List Length part 1 JS HTML DOM - DOM Node List Length part 2