Auto complete text field is similar to a drop down list, as a visitor types into the text field, a list of selectable options will appear. But this auto complete text field is not the same as a Combo Box.

To implement this auto complete text field, common.js and actb.js are required. These files can be downloaded from here.
Then do the following steps:

1. Firstly, include the .js file into your script
   

   <script type=”text/javascript” src=”library/actb/actb.js”></script>
   <script type=”text/javascript” src=”library/actb/common.js”></script>

2. Create a standard single line text field.
   

   <input type”text” id=”textbox_id”>

3. Create an array (in JavaScript) containing the keywords
   

   <script type=”text/javascript”>
   var customarray = new Array(‘apple’,'pear’,'mango’,'pineapple’,'orange’,'banana’,'durian’, ‘jackfruit’,'etc’);
   </script>

4. Apply the widget. This script must be created AFTER the text field is created.
   

   <script type=”text/javascript”>
   actb(document.getElementById(‘textbox_id’),customarray);
   </script>

And you’re done!