JavaScript could also be called event-driven. Hence it can respond to events. However, let’s first understand what events are.
- What are Events
- The onclick() Event
- The onsubmit() Event
- The mouseover() and mouseout() event
- List of HTML5 Events
1. What are Events
JavaScript code interacts with the HTML via events that are generated when a user or the browser manipulates the page.
For example, when the browser loads a page, this is an event. When a user clicks a button in a html page, this is also an event. Other events includes: pressing a key, resizing a window, closing a window etc.
Programmers can use these events as a trigger to execute a JavaScript code as a response. So when a user clicks on a button, the programmer specifies the codes to run. Generally this is a function as we learned in Tutorial 10.
Events in JavaScript are part of the Document Object Model (DOM) Level 3. Therefore, every HTML element contains a collection of events which can be used to trigger a JavaScript code.
Let’s start with an onclick() event
2. onclick() Event
The onclick() event happens when the mouse is clicked. This is the most frequently used event. You can actually put some validation code to run before the actual action is performed.
The example below demonstrates the onclick event
<html> <head> <title>Events Demo</title> <script type = "text/javascript"> <!-- function greetings() { alert("Good Morning") } //--> </script> </head> <body> <p>Click the following button and see result</p> <form> <input type = "button" onclick = "greetings()" value = "Good Morning" /> </form> </body> </html>
3. onsubmit() Event
This is is an event that occurs when you try to submit a form. Therefore, you can put some validation codes before the actual actions is performed.
For example, the code in the example below show the validation of a form when a submit button is clicked. Remember that if you click the submit button in a form, the data entered in the form is submitted to the server. Won’t it be great to validate the content of the form before you submit.
The example below illustrates this.
<html> <head> <title>Events Demo</title> <script type = "text/javascript"> <!-- function validation() { all validation goes here ......... return either true or false } //--> </script> </head> <body> <p>Click the following button and see result</p> <form method = "POST" action = "#" onsubmit = "return validate()"> ....... <input type = "submit" value = "Submit" /> </form> </body> </html>
4. onmouseover() and onmouseout() events
These are events used to create a hover effect when the mouse moves over a control on a html page. For example, you may want to brighten an images color when the mouse moves over it.
The onmouseover() event triggers when the moves over an element while onmouseout() triggers when the mouse moves out of the that element.
The example below illustrates this
<html> <head> <title>moouseover and mouseout Demo</title> <script type = "text/javascript"> <!-- function over() { document.write ("Mouse Over"); } function out() { document.write ("Mouse Out"); } //--> </script> </head> <body> <p>Take your mouse inside this section to see the outcome:</p> <div onmouseover = "over()" onmouseout = "out()"> <h2> This is inside the section </h2> </div> </body> </html>
5. List of HTML 5 Events
The table below provides a list of standard events in HTML5
Event/Attribute | Value | Brief Description |
---|---|---|
Offline | script | Triggers when the document goes offline. |
Onabort | script | Triggers on an abort event. |
onafterprint | script | Triggers after the document is printed |
onbeforeonload | script | Triggers before the document loads |
onbeforeprint | script | Triggers before the document is printed |
onblur | script | Triggers when the window loses focus |
oncanplay | script | Triggers when media can start play, but might has to stop for buffering |
oncanplaythrough | script | Triggers when media can be played to the end, without stopping for buffering |
onchange | script | Triggers when an element changes |
onclick | script | Triggers on a mouse click |
oncontextmenu | script | Triggers when a context menu is triggered |
ondblclick | script | Triggers on a mouse double-click |
ondrag | script | Triggers when an element is dragged |
ondragend | script | Triggers at the end of a drag operation |
ondragenter | script | Triggers when an element has been dragged to a valid drop target |
ondragleave | script | Triggers when an element is being dragged over a valid drop target |
ondragover | script | Triggers at the start of a drag operation |
ondragstart | script | Triggers at the start of a drag operation |
ondrop | script | Triggers when dragged element is being dropped |
ondurationchange | script | Triggers when the length of the media is changed |
onemptied | script | Triggers when a media resource element suddenly becomes empty. |
onended | script | Triggers when media has reach the end |
onerror | script | Triggers when an error occur |
onfocus | script | Triggers when the window gets focus |
onformchange | script | Triggers when a form changes |
onforminput | script | Triggers when a form gets user input |
onhaschange | script | Triggers when the document has change |
oninput | script | Triggers when an element gets user input |
oninvalid | script | Triggers when an element is invalid |
onkeydown | script | Triggers when a key is pressed |
onkeypress | script | Triggers when a key is pressed and released |
onkeyup | script | Triggers when a key is released |
onload | script | Triggers when the document loads |
onloadeddata | script | Triggers when media data is loaded |
onloadedmetadata | script | Triggers when the duration and other media data of a media element is loaded |
onloadstart | script | Triggers when the browser starts to load the media data |
onmessage | script | Triggers when the message is triggered |
onmousedown | script | Triggers when a mouse button is pressed |
onmousemove | script | Triggers when the mouse pointer moves |
onmouseout | script | Triggers when the mouse pointer moves out of an element |
onmouseover | script | Triggers when the mouse pointer moves over an element |
onmouseup | script | Triggers when a mouse button is released |
onmousewheel | script | Triggers when the mouse wheel is being rotated |
onoffline | script | Triggers when the document goes offline |
onoine | script | Triggers when the document comes online |
ononline | script | Triggers when the document comes online |
onpagehide | script | Triggers when the window is hidden |
onpageshow | script | Triggers when the window becomes visible |
onpause | script | Triggers when media data is paused |
onplay | script | Triggers when media data is going to start playing |
onplaying | script | Triggers when media data has start playing |
onpopstate | script | Triggers when the window’s history changes |
onprogress | script | Triggers when the browser is fetching the media data |
onratechange | script | Triggers when the media data’s playing rate has changed |
onreadystatechange | script | Triggers when the ready-state changes |
onredo | script | Triggers when the document performs a redo |
onresize | script | Triggers when the window is resized |
onscroll | script | Triggers when an element’s scrollbar is being scrolled |
onseeked | script | Triggers when a media element’s seeking attribute is no longer true, and the seeking has ended |
onseeking | script | Triggers when a media element’s seeking attribute is true, and the seeking has begun |
onselect | script | Triggers when an element is selected |
onstalled | script | Triggers when there is an error in fetching media data |
onstorage | script | Triggers when a document loads |
onsubmit | script | Triggers when a form is submitted |
onsuspend | script | Triggers when the browser has been fetching media data, but stopped before the entire media file was fetched |
ontimeupdate | script | Triggers when media changes its playing position |
onundo | script | Triggers when a document performs an undo |
onunload | script | Triggers when the user leaves the document |
onvolumechange | script | Triggers when media changes the volume, also when volume is set to “mute” |
onwaiting | script | Triggers when media has stopped playing, but is expected to resume |
We recommend you try out some of these events just to see how they work!