Using JavaScript to handle drop-down list selections






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