javascript - Populate one dropdown list based on another dropdown list

Question

I have two dropdown menus as follows:

<form id="dynamicForm">
  <select id="A">

  </select>
  <select id="B">

  </select>
</form>

And I have a dictionary object where the keys are the options for A and the values, B are arrays corresponding to each element in A, as follows:

var diction = {
    A1: ["B1", "B2", "B3"], 
    A2: ["B4", "B5", "B6"]
}

How can I dynamically populate the menu B based on what the user selects in menu A?

Answer 1

Bind a change event handler and populate second select tag based on selected value.

var diction = {
  A1: ["B1", "B2", "B3"],
  A2: ["B4", "B5", "B6"]
}

// bind change event handler
$('#A').change(function() {
  // get the second dropdown
  $('#B').html(
      // get array by the selected value
      diction[this.value]
      // iterate  and generate options
      .map(function(v) {
        // generate options with the array element
        return $('<option/>', {
          value: v,
          text: v
        })
      })
    )
    // trigger change event to generate second select tag initially
}).change()

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<form id="dynamicForm">
  <select id="A">
    <option value="A1">A1</option>
    <option value="A2">A2</option>
  </select>
  <select id="B">
  </select>
</form>