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Using JavaScript to handle drop-down list selections

, 25 Jul 2009 CPOL
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A simple method of making dropdown lists automatically navigate to a new page when a new selection is made.

Introduction

We've all seen sites that feature drop down lists that automatically take you to your selection without you needing to make the cumbersome and lengthy step of hitting a "Go" button. If you've ever wondered how they do this then as you probably expected it's very simple.   

What on Earth am I talking about?

Picture a drop down list as follows:

Screenshot - dropdown.png

We often see a button next to the list that the user should press in order to actually activate there selection:

Screenshot - dropdown2.png

The user selects the value from the dropdown, hits Go, and the choice is made. By using javascript we can have the list notify us when a change is made, and we can essentially hit that Go button for the user. Not only do we save the use all the hassle of clicking on a button, we also get a handy reduction in the amount of screen real estate used.

How do we do it?

A typical dropdown list is instantiated using the following:

<select name=select1>
<option>Value 1</option>
<option>Value 2</option>
<option>Value 3</option>
</select>

(Give or take some attributes). What we do is add an attribute that instructs the page to call our handler for when the list selection is changed.

<select name=select1 onchange='OnChange(this.form.select1);'>

Our handler will look up the value that has just been selected, and navigate to an appropriate URL. An example of this is shown below:

<SCRIPT LANGUAGE="javascript">
<!--
function OnChange(dropdown)
{
    var myindex  = dropdown.selectedIndex
    var SelValue = dropdown.options[myindex].value
    var baseURL  = <Some value based on SelValue>
    top.location.href = baseURL;
    
    return true;
}
//-->
</SCRIPT>

What if the user isn't using JavaScript?

We use the <noscript> tag to help us. We provide a Go button for the list, but only show it if JavaScript is not present:  

<select name=select1>
<option>Value 1</option>
<option>Value 2</option>
<option>Value 3</option>
</select><noscript><INPUT type="submit" value="Go" name=submit1></noscript>

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Chris Maunder
Founder CodeProject
Canada Canada
Chris is the Co-founder, Administrator, Architect, Chief Editor and Shameless Hack who wrote and runs The Code Project. He's been programming since 1988 while pretending to be, in various guises, an astrophysicist, mathematician, physicist, hydrologist, geomorphologist, defence intelligence researcher and then, when all that got a bit rough on the nerves, a web developer. He is a Microsoft Visual C++ MVP both globally and for Canada locally.
 
His programming experience includes C/C++, C#, SQL, MFC, ASP, ASP.NET, and far, far too much FORTRAN. He has worked on PocketPCs, AIX mainframes, Sun workstations, and a CRAY YMP C90 behemoth but finds notebooks take up less desk space.
 
He dodges, he weaves, and he never gets enough sleep. He is kind to small animals.
 
Chris was born and bred in Australia but splits his time between Toronto and Melbourne, depending on the weather. For relaxation he is into road cycling, snowboarding, rock climbing, and storm chasing.
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GeneralUsing JavaScript to handle drop-down list selections Pinmemberpadolsky11-Aug-09 5:58 

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