Harvard Extension School, Fall 2018
CSCI E-12 Fundamentals of Web Site Development

## JavaScript and Forms

### Exposing Additional Form Elements

Additional relevant form elements are exposed based upon user input. Here, this is achieved by having the entire form in the markup, with a certain section hidden via CSS (`display: none;`). If "Yes" is chosen, the display property is changed to "block" through JS.

Example 8.7 - Exposing Additional Form Elements - Example 8.7 (Without Styles) | <form method="get" name="ice_cream" id="ice_cream" action="http://cscie12.dce.harvard.edu/echo" enctype="application/x-www-form-urlencoded"><div> Would you like ice cream?<br/><input type="radio" name="want" id="ic_yes" value="yes" onclick="displayIceCreamOptions()"/><label for="ic_yes">Yes</label><br/><input type="radio" name="want" id="ic_no" value="no" onclick="displayIceCreamOptions()"/><label for="ic_no">No</label></div><fieldset id="icecream_options" style="display: none;"><legend>Ice Cream Options</legend><p>How would you like it?</p><input type="radio" id="container_cup" name="container" value="cup"/><label for="container_cup">Cup</label><br/><input type="radio" id="container_cone" name="container" value="cone"/><label for="container_cone">Cone</label><br/><p>Pick your toppings:</p><input type="checkbox" name="toppings" id="toppings_wc" value="whipcream"/><label for="toppings_wc">Whipped cream</label><br/><input type="checkbox" name="toppings" id="toppings_j" value="jimmies"/><label for="toppings_j">Jimmies</label><br/><input type="checkbox" name="toppings" id="toppings_nuts" value="nuts"/><label for="toppings_nuts">Nuts</label><br/><input type="checkbox" name="toppings" id="toppings_cherry" value="cherry"/><label for="toppings_cherry">Cherry</label></fieldset><p><input type="submit"/></p></form>#icecream_options { display:none; background-color: #eee; margin-left: 2em; }function displayIceCreamOptions() { var divico = document.getElementById('icecream_options'); var inputYes = document.getElementById('ic_yes'); if (inputYes.checked == true) { divico.style.display = 'block'; } else { divico.style.display = 'none'; } }

- Markup
- Style
- Script
- Screenshot

    <form method="get" name="ice_cream" id="ice_cream" action="http://cscie12.dce.harvard.edu/echo">
    <div>Would you like ice cream?<br/>
    <input type="radio" name="want" id="ic_yes" value="yes" onclick="displayIceCreamOptions()"/><label for="ic_yes">Yes</label><br/>
    <input type="radio" name="want" id="ic_no" value="no" onclick="displayIceCreamOptions()"/><label for="ic_no">No</label></div><fieldset id="icecream_options" style="display: none;"><legend>Ice Cream Options</legend><p>How would you like it?</p>

    <input type="radio" id="container_cup" name="container" value="cup"/><label for="container_cup">Cup</label><br/>
    <input type="radio" id="container_cone" name="container" value="cone"/><label for="container_cone">Cone</label><br/><p>Pick your toppings:</p>

    <input type="checkbox" name="toppings" id="toppings_wc" value="whipcream"/><label for="toppings_wc">Whipped cream</label><br/>
    <input type="checkbox" name="toppings" id="toppings_j" value="jimmies"/><label for="toppings_j">Jimmies</label><br/>
    <input type="checkbox" name="toppings" id="toppings_nuts" value="nuts"/><label for="toppings_nuts">Nuts</label><br/>
    <input type="checkbox" name="toppings" id="toppings_cherry" value="cherry"/><label for="toppings_cherry">Cherry</label></fieldset><p>
    <input type="submit"/></p>

    </form>

In `style` element (`<style type="text/css">`) within `head` element:

    #icecream_options {
        display:none;
        background-color: #eee;
        margin-left: 2em;
    }

In `script` element within `head` element (`<script type="text/javascript">`):

    function displayIceCreamOptions() {
        var divico = document.getElementById('icecream_options');
        var inputYes = document.getElementById('ic_yes');
        if (inputYes.checked == true) {
          divico.style.display = 'block';
        } else {
          divico.style.display = 'none';
        }
    }

Copyright © David Heitmeyer