Check box Object, dom Checkbox events - Javascript (JS) Tutorial

Tutorials

Javascript

Topic

How to change checkbox selection using javascript?
or
What are the events associated with checkbox?

Explanation

Basics of HTML form checkbox

The following syntax will get the check box object in javascript
Syntax: document.formname.checkboxname

Example Code:
<form name=testform>
<input name=cb1 value=test type=checkbox>
<input name=cb2 value=test2 type=checkbox>
</form>

<script language="javascript">
var cbobject= document.testform.cb1;
</script>

The object cbobject is an array of check box element. To use the first check box, we have to call cbobject[0], for second box it is cbobject[1] and so on.. Here are the events, dom properties and method associated with checkbox element.

Event Handlers: Associated with Form type Check Box:
All the examples below use a javascript function output
<script language=javascript>
function output()
{
alert("testing checkbox events");
}
</script>

Event Handler	Description	Example
onMouseOver	This is invoked when a mouse is moved over the checkbox	<input type=checkbox onMouseOver="output()"> Result: CB1
onMouseDown	This is invoked when a mouse is pressed down on the checkbox	<input type=checkbox onMouseDown="output()"> Result: CB1
onMouseUp	This is invoked when a mouse is pressed down on the checkbox and released	<input type=checkbox onMouseUp="output()"> Result: CB1
onClick	onClick is invoked when a mouse click is done on the checkbox	<input type=checkbox onClick="output()"> Result: CB1
onBlur	Executes some code when the check box loses focus using tab	<input type=checkbox onBlur="output()"> Result: CB1
onFocus	Executes some code when the check box gets the focus using tab	<input type=checkbox onFocus="output()"> Result: CB1

DOM Properties:
The following are the list of DOM (Dynamic Object Model) properties that can be used to get and alter checkbox properties in javascript.
The below examples are based on the form
<form name=testb>
<input name=mycb type=checkbox value=111> box1
<input name=mycb type=checkbox value=222> box2
</form>

DOM Property	Description	Example
checked	Used to check or select checkbox. Each element has to be checked individually. The element if selected will return true else false.	To Check: var ss = document.testb.mycb[0].checked; var ss1 = document.testb.mycb[1].checked; To Select: document.testb.mycb[0].checked = true;
defaultChecked	Used to check whether the check box is selected by default	To Get: var ss = document.testb.mycb[0].defaultChecked;
form	Used to get the parent node (form object) of this check box	To Get: var ss = document.testb.mycb[0].form;
name	Used to get checkbox name	To Get: var ss = document.testb.mycb[0].name;
type	Used to get form type	To Get: var ss = document.testb.mycb[0].type;
value	Used to set or get checkbox value	To Get: var ss = document.testb.mycb[0].value; To Set:: document.testb.mycb[0].value = "testy";

DOM Methods:
The following are the list of DOM (Dynamic Object Model) methods that can be used to do dynamic changes like dynamic check box selection, using javascript.

DOM Method	Description	Example
click()	Used to dynamically make a checkbox checked	To Click: document.testb.mycb.click();
blur()	Used to dynamically make the check box blur	To Blur: document.testb.mycb.blur();
focus()	Used to dynamically get focus on the check box	To Focus: document.testb.mycb.focus();

Example: Making Check Box Select on Mouse Over

Result: