码农教程 - 一技在手,衣食无忧! tools

目录

How TO - Cascading Dropdown List

❮ Previous Next ❯

Learn how to create a cascading dropdown list with JavaScript.

Try it Yourself »

Create Three Dropdown Lists

Create three dropdown lists, inside an HTML form.

The second and third dropdown list will display different options, depending on the value selected in the parent dropdown list.

Step 1) Add HTML:

Example

<form name="form1" id="form1" action="/action_page.html">
  Subjects: <select name="subject" id="subject">
    <option value="" selected="selected">Select subject</option>
  </select>
  <br><br>
  Topics: <select name="topic" id="topic">
    <option value="" selected="selected">Please select subject first</option>
  </select>
  <br><br>
  Chapters: <select name="chapter" id="chapter">
    <option value="" selected="selected">Please select topic first</option>
  </select>
  <br><br>
  <input type="submit" value="Submit">
</form>
Step 2) Add JavaScript:

Example

var subjectObject = {
  "Front-end": {
    "HTML": ["Links", "Images", "Tables", "Lists"],
    "CSS": ["Borders", "Margins", "Backgrounds", "Float"],
    "JavaScript": ["Variables", "Operators", "Functions", "Conditions"]
  },
  "Back-end": {
    "PHP": ["Variables", "Strings", "Arrays"],
    "SQL": ["SELECT", "UPDATE", "DELETE"]
  }
}
window.onload = function() {
  var subjectSel = document.getElementById("subject");
  var topicSel = document.getElementById("topic");
  var chapterSel = document.getElementById("chapter");
  for (var x in subjectObject) {
    subjectSel.options[subjectSel.options.length] = new Option(x, x);
  }
  subjectSel.onchange = function() {
    //empty Chapters- and Topics- dropdowns
    chapterSel.length = 1;
    topicSel.length = 1;
    //display correct values
    for (var y in subjectObject[this.value]) {
      topicSel.options[topicSel.options.length] = new Option(y, y);
    }
  }
  topicSel.onchange = function() {
    //empty Chapters dropdown
    chapterSel.length = 1;
    //display correct values
    var z = subjectObject[subjectSel.value][this.value];
    for (var i = 0; i < z.length; i++) {
      chapterSel.options[chapterSel.options.length] = new Option(z[i], z[i]);
    }
  }
}
Try it Yourself »

Tip: Go to our CSS Dropdowns Tutorial to learn more about dropdowns.

Tip: Go to our Hoverable Dropdowns to learn more about hoverable dropdowns.


❮ Previous Next ❯