Javascript Example
Screen shot
Javascript Select All/Unselect All checkbox

<html>
<head>
<title>Javascript Example</title>

<script language=\"javascript\" type=\"text/javascript\">

function checkall(objForm)
{
    len = objForm.elements.length;
    var i=0;
    for( i=0 ; i<len ; i++){
        if (objForm.elements[i].type==\'checkbox\')
        objForm.elements[i].checked=objForm.check_all.checked;
    }
}

</script>
</head>

<body>
<form name=\"frm\" action=\"\" method=\"post\" onSubmit=\"return validate();\">

Select All <input name=\"check_all\" type=\"checkbox\"   id=\"check_all\" onClick=\"checkall(this.form)\" value=\"check_all\" /><br><br>

Play Football<input name=\"hobby1\" type=\"checkbox\" value=\"play_football\" /><br>
Play Music<input name=\"hobby2\" type=\"checkbox\" value=\"play_music\" /><br>
Listen Music<input name=\"hobby3\" type=\"checkbox\" value=\"listen_music\" /><br>
Reading Newspaper<input name=\"hobby4\" type=\"checkbox\" value=\"reading_newspaper\" />

<div id=\"msg\" style=\"color:#FF0000\"></div>

</form>
</body>
</html>

You can download source code here