HTML Form Tutorial, Part I
This is the first of a 2-part article.
HTML web page forms are a means of collecting information. People fill in a form and/or select something. Then they click a button. (There are ways to cause a form to be submitted without the user clicking a button. Those are, however, outside the scope of this 2-part article.)
Forms don't actually process information. They merely provide the means to collect information for submission to form information processing software.
For something to be done with the information, it must be sent somewhere. Information can be processed by CGI programs, PHP pages, JavaScript functions, and mailto: links.
This tutorial is about how to make forms and how to send the information, but not how to process the information after it has been sent off.
Building a Web Page Form
Forms begin with the <form> tag and end with the </form> tag. The <form> tag can contain several attributes.
Sometimes you'll need to determine the applicable attributes. Other times, installation directions accompanying from processing software will specify the <form> tag attributes expected by the installation.
Be that as it may, we'll address form tag attributes so you have in information you need to make determinations.
Where Form Submitted Information Is Sent
The <form> tag attribute that specifies where the information will be sent is the action attribute.
Sending Form Information To CGI Programs
If the information is being sent to a CGI program on the same domain as the web page containing the form, the action attribute may contain either a relative URL or an absolute URL. With a relative URL, it would look something like this:
action="/cgi-bin/something.cgi"
However, if the information is being sent to a CGI program on a different domain, the URL must be absolute (a complete http://... URL):
action="http://domain.com/cgi-bin/something.cgi"
Sending Form Information To PHP Page
The procedure for sending form information to PHP pages is similar to sending it to CGI programs. The URL of the form's action attribute is the URL of the PHP page where the form information is to be sent.
Sending Form Information To JavaScript Functions
When sending form information to a JavaScript function, the action attribute would look something like:
action="javascript:SomeFunction()"
or, the action attribute might be replaced with the JavaScript specific onclick attribute:
onclick="return SomeFunction()"
If the form information is to be sent to both a JavaScript function and to a CGI program, then both the action and the onclick attributes would be specified.
Sending To mailto: Links
To send form information to the visitor's email program, with the To: destination already filled in, use:
action="mailto:name@domain.com"
If you also want to specify a subject for the email:
action="mailto:name@domain.com?subject=My%20Subject"
(Use "%20" instead of spaces when specifying a subject.)
Note that not all browsers recognize the mailto: link. It is suggested you use this only as a last resort.
How Form Submitted Information Is Sent
Another <form> tag attribute specifies how the information will be sent to wherever it's going. That's the method attribute. The method attribute is either
method="POST"
or
method="GET"
Which you use depends on how the destination program or function wants to receive the information.
Sending With Method GET
method="GET" is used if you want to send information somewhere via a browser URL. You've seen URLs that send information; they look something like:
http://domain.com/something.cgi?color=red&shape=round
In the above URL, the part after the question mark is information sent to something.cgi. Multiple information chunks are separated with an ampersand.
The GET method can send only a limited amount of information. The limitation depends on the server where the current web page is on and the server where the information is sent to. The limitation can be as little as 256 bytes but is often 1k or more.
Another limitation of the GET method is that the information being sent is visible in the browser's address bar. In some cases this is of no consequence. In others, it is unacceptable.
Some CGI programs are written to accept information via the GET or the POST method, some to accept only one or the other.
Sending With Method POST
method="POST" is the most common method used to send information from a form to information processing software.
The POST method can send much more information than the typical GET method. Browsers may limit the amount of POST information to 32k.
With POST, the information is not sent via the URL. Instead, it is sent as content invisible to the form user.
Specifying the Encoding Method for the Information Being Sent
The final <form> tag attribute we'll cover in this tutorial specifies how the form information will be encoded before sending it to wherever it's going. That's the enctype attribute.
The browser encodes the form information depending on the enctype attribute. Encoding transforms special non-alphanumeric characters that could otherwise wreak havoc during transmission or upon receipt into a series of characters that the receiving program or function can recognize. Encoding also inserts separators between the information chunks.
Often you don't have to concern yourself with the enctype. If you do not specify one, the default is assumed.
The default enctype attribute is:
enctype="application/x-www-form-urlencoded"
If your form includes file uploads, you will need
enctype="multipart/form-data"
And, if you will be using a mailto: link in the action attribute, your email body text will be less jumbled if you use
enctype="text/plain"
Form Related Tags
Between the <form> and </form> tags are the tags that create the body of the form. These are <select> (for drop-down lists and list boxes), <textarea> (for multi-line text areas), and <input> (for the rest).
Every form related tag has a name attribute. The name attribute is not required to build the form but may be necessary for the software the information will be submitted to.
The assigned name is sent with the information and helps the receiving software identify the information chunks it receives.
Some receiving software programs are okay with tag names containing spaces; some are not. If you don't know whether or not it is okay to use spaces in your form's tag names, use underscore characters instead of spaces. Underscore characters are almost always okay within tag names so long as the name doesn't start or end with an underscore.
Here is an example name attribute:
name="my_tag_name"
The <input> Tag
Most of the information forms collect is specified by the <input> tag. Single-line text entry fields, checkboxes, radio selections, password entry fields, form buttons, file upload fields, and image buttons are all specified with the <input> tag.
Every input tag requires a type attribute.
The "type" Attribute
The type attribute tells the browser what type of form field or button to create. The type attribute looks something like this:
type="_______"
with the underscore representing one of numerous types of type attributes.
— The type="submit" Attribute
A submit button is created with the type="submit" attribute. It might or might not have a value attribute, depending on whether or not you want to specify the text of the button. Also, the submit button might or might not have a name, depending on what the information receiving software's requirements are.
In this example, it does not have a name but it does have a value:
<form method="POST" action="/cgi-bin/something.cgi"> <input type="submit" value="Click Me!" /> </form>
Forms may contain more than one submit button. In that case, it is usual for the attributes to have names so the processing program or function knows which of them was clicked. Example:
<form method="POST" action="/cgi-bin/something.cgi"> <input type="submit" name="1" value="First Visit" /> <input type="submit" name="2" value="Second Visit" /> <input type="submit" name="3" value="Third Visit" /> </form>
— The type="text" Attribute
The type="text" attribute is a common form input field. It creates a place wherein a line of information can by typed.
If you want to put default text into the input field, use the value attribute. Example:
value="http://"
Both a size and a maxlength attribute may be used. These specify the size of the text input area and the maximum number of characters that may be typed into the input field. You may use neither, one, or both of those tags.
Here is an example:
<form method="POST" action="/cgi-bin/something.cgi"> <input type="text" name="url" size="17" maxlength="44" /> <input type="submit" /> </form>
— The type="password" Attribute
The type="password" attribute works the same as the type="text" attribute except the characters typed into the input area are displayed as asterisks. Here is an example:
<form method="POST" action="/cgi-bin/something.cgi"> <input type="password" name="P" size="9" maxlength="20" /> <input type="submit" /> </form>
— The type="checkbox" Attribute
The checkbox either contains information or it doesn't, depending on whether or not it is checked. Checkbox tags almost always have a value attribute.
If you want any checkboxes pre-checked, include the checked="checked" attribute. Example:
<form method="POST" action="/cgi-bin/something.cgi">
<input type="checkbox" name="c_blue" value="yes" />
<input type="checkbox" name="c_red"
value="yes" checked="checked" />
<input type="checkbox" name="c_pink"
value="yes" checked="checked" />
<input type="checkbox" name="c_yellow" value="yes" />
<input type="submit" />
</form>
In the above example, the user will see four checkboxes with the middle two pre-checked.
Notice that each checkbox has a different name. This separates the information into different chunks for the receiving software to process. In some cases, the receiving software might require the checkboxes to have the same name, but do it that way only if instructed to do so.
— The type="radio" Attribute
The value of only one radio button in a set is sent to the receiving software, the one that is checked. Radio tags almost always have a value attribute.
If you want to pre-check one radio button, use the checked="checked" attribute:
<form method="POST" action="/cgi-bin/something.cgi">
<input type="radio" name="color" value="blue" />
<input type="radio" name="color"
value="red" checked="checked" />
<input type="radio" name="color" value="pink" />
<input type="submit" />
</form>
In the above example, the user will see three radio buttons with the middle one pre-checked.
Each radio button in a set must have the same name. When more than one radio button has the same name, only one of them can be checked at a time.
— The type="file" Attribute
To upload a file from the user's computer to the form information processing software, the type="file" attribute is used. (To use this attribute, the <form> tag must have the enctype attribute specified as "multipart/form-data")
Optionally, you may restrict the type of file the user may upload with the accept attribute. The accept attribute specifies a MIME Content Type. There are many MIME types and to list them all would be space prohibitive. However, here are those you are most likely to need.
To restrict the uploads to images, use:
accept="image/*"
To restrict to only GIF images, use:
accept="image/gif"
To specify only JPEG, PNG, or TIFF image files, use "image/jpg,jpeg", "image/png", or "image/tiff", respectively. To specify GIF and JPEG, use "image/gif,jpg,jpeg"
To restrict to text files only, use:
accept="text/*"
To specify HTML files or plain text files, use "text/html" or "text/plain", respectively.
Optionally, you may specify the size of the input field and the maximum number of characters that may be entered with the size and maxlength attributes.
Here is an example file upload form input area:
<form method="POST"
action="/cgi-bin/something.cgi"
enctype="multipart/form-data">
<input type="file" name="upfile" accept="image/*" />
<input type="submit" />
</form>
— The type="hidden" Attribute
Use the type="hidden" attribute to specify information for the receiving software that the user may not change and to keep it invisible. This information is usually required by the software in order to process the other information and/or to determine what to send back to the browser. The installation instructions of the program or function should specify what hidden fields are required, if any.
Here is an example:
<form method="POST" action="/cgi-bin/something.cgi">
<input type="hidden"
name="nextpage"
value="http://example.com/" />
<input type="submit" value="Click For Next Page" />
</form>
— The type="reset" Attribute
This attribute creates a reset button. Clicking that button will reset the form to the state it was in when it was first loaded into the browser. It might or might not have a value attribute, depending on whether or not you want to specify the text of the button. It rarely requires a name because the reset button's value is rarely used by the receiving program or function.
In this example, it does not have a name but it does have a value:
<form method="POST" action="/cgi-bin/something.cgi"> <input type="text" name="url" size="17" maxlength="44" /> <input type="reset" value="Erase Everything!" /> <input type="submit" value="Submit Now!" /> </form>
— The type="button" Attribute
This attribute creates a clickable button with text you specify in the value attribute. This type of button is typically used to send information to a JavaScript function with the onclick attribute. In this case, a submit button may be optional. Example:
<form method="POST" action="/cgi-bin/something.cgi">
<input type="text" name="email" size="17" maxlength="44" />
<input type="button"
value="Verify Email Address"
onclick="return EmailVerification()" />
<input type="submit" />
</form>
— The type="image" Attribute
An image may be used instead of a submit button. To do so, use the type="image" attribute.
When using the type="image" attribute, the "src" attribute must be specified. The src attribute is specified like you would specify the src attribute in an <img> tag to place an image on a web page. Optionally, you may include align, border, height, width, hspace, and/or vspace attributes, just like you would in an <img> tag.
When the user clicks the image, the form submits its information to the program or function specified in the <form> tag.
Here is an example:
<form method="POST" action="/cgi-bin/something.cgi">
<input type="text" name="url" size="17" maxlength="44" />
<input type="image"
src="myimage.gif"
border="0"
align="right" />
</form>
Part II
Part II of this tutorial (HTML Form Tutorial, Part II) introduces the <textarea>, <select>, and <option> tags. It will also have some other goodies, including a complete form with the tags mentioned in this tutorial.
Will Bontrager
