Pre-populate combo values

This sample is to populate combo values in html form using javascript.

For manually insertion of the Option values into the combobox.

<script type="text/javascript"> 
function prepopulate(reportType){
    document.form1.report_view.options.length = 0;
    if (reportType ==  "Pie_Chart" || reportType == "Bar_Graph"){
        document.form1.report_view.options[0] = new Option("Adobe Reader (.pdf)","pdf");
        document.form1.report_view.options[1] = new Option("Open Office (.odt)","odt");
    }else{
        document.form1.report_view.options[0] = new Option("Adobe Reader (.pdf)","pdf");
        document.form1.report_view.options[1] = new Option("Microsoft Excel (.xls)","xls");
        document.form1.report_view.options[2] = new Option("Open Office (.odt)","odt");
    }
}
</script>

In the html part:

<select name="report_type" id = "report_type" onChange="javascript:prepopulate(this.value)">
    <option value="Consolidated_Comments">Consolidated Comments</option>
    <option value="Pie_Chart">Consolidated Result - Pie Chart</option>
    <option value="Bar_Graph">Consolidated Result - Bar Graph</option>
    <option value="Individual_Results_Comments">Individual Results (Comments)</option>
    <option value="Individual_Results_FreeText">Individual Results (Free Text)</option>
    <option value="List_of_Questions">List of Questions</option>
    <option value="Individual_Comment">Individual Result</option>
</select>
<select name="report_view">
</select>

Whenever the report type selected is bar graph or pie chart, it will not display the excel report view, else it will return all three report views.

reference: here