20 html-forms

HTML Forms

Mar 14, 2013

What are forms?
 <form> is just another kind of HTML tag
 HTML forms are used to create (rather primitive) GUIs on Web
pages
 Usually the purpose is to ask the user for information
 The information is then sent back to the server
 A form is an area that can contain form elements
 The syntax is: <form parameters> ...form elements... </form>
 Form elements include: buttons, checkboxes, text fields, radio buttons,
drop-down menus, etc
 Other kinds of HTML tags can be mixed in with the form elements
 A form usually contains a Submit button to send the information in he
form elements to the server
 The form’s parameters tell JavaScript how to send the information to the
server (there are two different ways it could be sent)
 Forms can be used for other things, such as a GUI for simple programs
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Forms and JavaScript
 The JavaScript language can be used to make pages that “do
something”
 You can use JavaScript to write complete programs, but...
 Usually you just use snippets of JavaScript here and there throughout your
Web page
 JavaScript code snippets can be attached to various form elements
 For example, you might want to check that a zipcode field contains a 5-digit
integer before you send that information to the server
 Microsoft sometimes calls JavaScript “active scripting”
 HTML forms can be used without JavaScript, and JavaScript can
be used without HTML forms, but they work well together
 JavaScript for HTML is covered in a separate lecture

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The <form> tag
 The <form arguments> ... </form> tag encloses form
elements (and probably other HTML as well)
 The arguments to form tell what to do with the user input
 action="url" (required)
 Specifies where to send the data when the Submit button is clicked
 method="get" (default)
 Form data is sent as a URL with ?form_data info appended to the end
 Can be used only if data is all ASCII and not more than 100 characters
 method="post"
 Form data is sent in the body of the URL request
 Cannot be bookmarked by most browsers
 target="target"
 Tells where to open the page sent as a result of the request
 target= _blank means open in a new window
 target= _top means use the same window

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The <input> tag
 Most, but not all, form elements use the input tag, with a
type="..." argument to tell which kind of element it is
 type can be text, checkbox, radio, password, hidden, submit, reset,
button, file, or image
 Other common input tag arguments include:
 name: the name of the element
 value: the “value” of the element; used in different ways for different
values of type
 readonly: the value cannot be changed
 disabled: the user can’t do anything with this element
 Other arguments are defined for the input tag but have meaning only for
certain values of type

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Text input
A text field:
<input type="text" name="textfield" value="with an initial value">

A multi-line text field
<textarea name="textarea" cols="24" rows="2">Hello</textarea>

A password field:
<input type="password" name="textfield3" value="secret">

• Note that two of these use the input tag, but one uses textarea
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Buttons
 A submit button:
<input type="submit" name="Submit" value="Submit">
 A reset button:
<input type="reset" name="Submit2" value="Reset">
 A plain button:
<input type="button" name="Submit3" value="Push Me">

 submit: send data

 reset: restore all form elements to
their initial state
 button: take some action as

• Note that the type is input,specified by JavaScript
not “button”
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Checkboxes
 A checkbox:
<input type="checkbox" name="checkbox”
value="checkbox" checked>

 type: "checkbox"
 name: used to reference this form element from JavaScript
 value: value to be returned when element is checked
 Note that there is no text associated with the checkbox—
you have to supply text in the surrounding HTML

8

Radio buttons
Radio buttons:<br>
<input type="radio" name="radiobutton" value="myValue1">
male<br>
<input type="radio" name="radiobutton" value="myValue2" checked>
female

 If two or more radio buttons have the same name, the user can
only select one of them at a time
 This is how you make a radio button “group”
 If you ask for the value of that name, you will get the value
specified for the selected radio button
 As with checkboxes, radio buttons do not contain any text
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Drop-down menu or list
 A menu or list:
<select name="select">
<option value="red">red</option>
<option value="green">green</option>
<option value="BLUE">blue</option>
</select>

 Additional arguments:
 size: the number of items visible in the list (default is "1")
 multiple: if set to "true", any number of items may be selected
(default is "false")

10

Hidden fields
 <input type="hidden" name="hiddenField" value="nyah">
<-- right there, don't you see it?

 What good is this?
 All input fields are sent back to the server, including hidden fields
 This is a way to include information that the user doesn’t need to see (or
that you don’t want her to see)
 The value of a hidden field can be set programmatically (by JavaScript)
before the form is submitted

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A complete example
<html>
<head>
<title>Get Identity</title>
<meta http-equiv="Content-Type" content="text/html;
charset=iso-8859-1">
</head>
<body>
<p><b>Who are you?</b></p>
<form method="post" action="">
<p>Name:
<input type="text" name="textfield">
</p>
<p>Gender:
<input type="radio" name="gender" value="m">Male
<input type="radio" name="gender" value="f">Female</p>
</form>
</body>
</html>

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20 html-forms

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