Question

I have two select’s. The values/text of the second one will vary based on what is selected in the first select.

I will have onchange function linked to the first select. But I do not know

• how I can save data for my onchange function in html
• how I can change second select html definition (text/values + number of options) in my javascript code

Note that I don’t want to use any javascript framework

Answer 1

1) I assume you’re seeking advice on how to encode the data for the second select input. I suggest using JavaScript to store a mapping of possible values of the first select to value to be used by the second so you can index it directly, e.g.:

// Assume "select1" can have option values "English" and "Spanish".
var select2data = {
  'English': [['One', 1], ['Two', 2], ['Three', 3]],
  'Spanish': [['Uno', 1], ['Dos', 2], ['Tres', 3]]
};

This strategy is nice concise but requires programmatic generation of JavaScript. If you really want to use plain HTML then you could have a nested DIV structure and parse it as needed, e.g.:

<div id="select2data" style="display:none">
  <div id="English">
    <div><div>One</div><div>1</div></div>
    <div><div>Two</div><div>2</div></div>
    ...
  <div id="Spanish">
  ...
<script type="text/javascript">
  var s2d = document.getElementById("select2data")
    , select2data = {};
  for (var i=0; i<s2d.children.length; i++) { // Each of "id=English", etc.
    var data=s2d.children[i], opts=[];
    for (var j=0; j<data.children.length; j++) {
      opts.push(new Option(data.children[j].children[0].firstChild,
                           data.children[j].children[1].firstChild));
    }
    select2data[data.id] = opts;
  }
</script>

2) Now, setting the options of select2 can be done by looking up the data from the value of select1, encoding them as DOM Option objects, and adding them to select1:

var sel1 = document.getElementById('select1')
  , sel2 = document.getElementById('select2');
sel1.onchange = function() {
  var os = select2data[sel1.value]; // Get the options required by select1.
  if (os) {
    sel2.options.length = 0; // Clear the options for select2.
    for (var i=0; i<os.length; i++) {
      var o = new Option(os[i][0], os[i][1]);
      try { // Add each option, allowing for browser differences.
        sel2.add(o);
      } catch (ex) {
        sel2.add(o, null);
      }
    }
    sel2.selectedIndex = 0;
  }
  return true;
};

Note that this is all untested and has lots of room for improvement but should illustrate the idea.