An Easy Way to Build Replacement Combo Boxes - Adding JavaScript
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Finally, we need to add a little basic JavaScript to control the opening and closing of the options div, and to add the selection made by the visitor to the text field. In a new file in your text editor begin with the following:
var comboopenflag;
function init() {
var combo = document.getElementById('combofield').value = "";
comboopenflag = "off";
}
This is called on the onload event of the body of the page. It ensures the options div is not open and sets the flag appropriately. This is needed after, say, a page refresh (it's not likely halfway through filling out a form, but it can happen). Our next function will open the div, or close it if it is already open and is called from the onclick event of the image used as the drop-down arrow:
function showOptions() {
if (comboopenflag != "on") {
document.getElementById('combodiv').style.display = "block";
comboopenflag = "on";
} else if (comboopenflag = "on") {
document.getElementById('combodiv').style.display = "none";
comboopenflag = "off";
}
}
This uses the flag to determine whether or not the div is currently open, and reverses its state, so when it is closed, it gets opened, and when it is opened it get closed. Finally, we need to get the selected option into the text field:
function setOption(selection) {
var combo = document.getElementById('combofield').value = selection;
document.getElementById('combodiv').style.display = "none";
comboopenflag = "off";
}
This accepts the parameter sent by the onclick event in the HTML file and uses this to add its value to the text field. Simple. It also closes off the options div. Save the file as combo.js in the same location as the HTML and CSS files.
If you view the page in either IE or FireFox, the box should function exactly as a combo box would, and work consistently across the two major vendors. I've only used very basic styling here to illustrate the point, but I'm sure you can see the potential of this technique. As I mentioned at the start of the article, this is the easy way to do it and is suitable only for small combo boxes with few options.
Hard-coding the options into the onclick event call has its limitations. In the next article, I'll be looking at a method that is better put to use with larger combo boxes with many options as well as a way of getting rid of the hard-coded values.
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