HTTP Forms

One of the earliest (and still widely used) mechanisms for transferring data from a browser (client) to the server is a form. The <form> is a specific HTML element that contains input fields and buttons the user can interact with.

The <input> Element

Perhaps the most important - and versatile - of these is the <input> element. By setting its type attribute, we can represent a wide range of possible inputs, as is demonstrated by this table taken from the MDN Web Docs:

<input type="button" name="ExampleButton" value="Click Me!"/>

<label><input type="checkbox" name="ExampleCheckbox"/><label>

<input type="color" name="ExampleColor" style="width: 40px; height: 40px;"/>

<input type="date" name="ExampleDate"/>

<input type="datetime-local" name="ExampleDatetimeLocal"/>

<input type="email" name="ExampleEmail"/>

<input type="file" name="ExampleFile"/>

<input type="hidden" name="ExampleHidden" value="f0321dc35"/>

<input type="image" name="ExampleImage" src="/images/button.png">}}"/>

<input type="number" name="ExampleNumber" min=0 max=10 step=1/>

<input type="password">

<label>
  <input type="radio" name="ExampleRadio" value="1"/>
  Choice One
</label>
<label>
  <input type="radio" name="ExampleRadio" value="2"/>
  Choice Two
</label>
<label>
  <input type="radio" name="ExampleRadio" value="3"/>
  Choice Three
</label>
      

<input type="range" name="ExampleRange" min="0" max="25"/>

<input type="reset" name="ResetExample"/>

<input type="search" name="ExampleSearch"/>

<input type="submit" name="ExampleSubmit" value="Save Changes"/>

<input type="tel" name="ExampleTel"/>

<input type="text" name="ExampleText"/>

<input type="time" name="ExampleTime"/>

<input type="url" name="ExampleUrl">

Regardless of the type, the <input> element also has a name and value property. The name is similar to a variable name, in that it is used to identify the input’s value when we serialize the form (more about that later), and the value is the value the input currently is (this starts as the value you specify in the HTML, but it changes when the user edits it).

Additionally, checkboxes and radio buttons have a boolean ischecked property. These indicate if the box/button is checked or not (and that the box/button’s value should be submitted).

The <textarea> Element

The <textarea> element represents a multi-line text input. Similar to terminal programs, this is represented by columns and rows, the numbers of which are set by the cols and rows attributes, respectively. Thus:

<textarea cols=40 rows=5></textarea>

Would look like:

As with inputs, a <textarea> has a name and value attribute.

The <select> Element

The <select> element, along with <option> and <optgroup> make drop-down selection boxes. The <select> takes a name attribute, while each <option> provides a different value. The <options> can further be nested in <optgroup>s with their own labels. The <select> also has a multiple attribute (to allow selecting multiple options), and size which determines how many options should be displayed at once (with scrolling if more are available).

For example:

<select id="dino-select">
    <optgroup label="Theropods">
        <option>Tyrannosaurus</option>
        <option>Velociraptor</option>
        <option>Deinonychus</option>
    </optgroup>
    <optgroup label="Sauropods">
        <option>Diplodocus</option>
        <option>Saltasaurus</option>
        <option>Apatosaurus</option>
    </optgroup>
</select>

Displays as:

The <label> Element

A <label> element represents a caption for an element in the form. It can be tied to a specific input using its for attribute, by setting its value to the id attribute of the associated input. This allows screen readers to identify the label as belonging to the input, and also allows browsers to give focus or activate the input element when the label is clicked.

For example, if you create a checkbox with a label:

<fieldset style="display:flex; align-items:center;">
  <input type="checkbox" id="example"/>
  <label for="example">Is Checked</label>
</fieldset>

Clicking the label will toggle the checkbox!

The <fieldset> Element

The <fieldset> element is used to group related form parts together, which can be captioned with a <legend>. It also has a for attribute which can be set to the id of a form on the page to associate with, so that the fieldset will be serialized with the form (this is not necessary if the fieldset is inside the form). Setting the fieldset’s disabled attribute will also disable all elements inside of it.

For example:

<fieldset>
  <legend>Who is your favorite muppet?</legend>
  <input type="radio" name="muppet" id="kermit">
    <label for="kermit">Kermit</label>
  </input>
  <input type="radio" name="muppet" id="animal">
    <label for="animal">Animal</label>
  </input>
  <input type="radio" name="muppet" id="piggy">
    <label for="piggy">Miss Piggy</label>
  </input>
  <input type="radio" name="muppet" id="gonzo">
    <label for="gonzo">Gonzo</label>
  </input>
</fieldset>

Would render:

The <form> Element

Finally, the <form> element wraps around all the <input>, <textarea>, and <select> elements, and gathers them along with any contained within associated <fieldset>s to submit in a serialized form. This is done when an <input type="submit"> is clicked within the form, when the enter key is pressed and the form has focus, or by calling the submit() method on the form with JavaScript.

There are a couple of special attributes we should know for the <form> element:

• action - the URL this form should be submitted to. Defaults to the URL the form was served from.
• enctype - the encoding strategy used, discussed in the next section. Possible values are:
  • application/x-www-form-urlencoded - the default
  • multipart/form-data - must be used to submit files
  • text/plain - useful for debugging
• method - the HTTP method to submit the form using, most often GET or POST

When the form is submitted, the form is serialized using the enctype attribute and submitted using the HTTP method to the URL specified by the action attribute. Let’s take a deeper look at this process next.