Transcript Powerpoint set "e" - University of Virginia Information Technology

More JavaScript, HTML Forms,
CGI Scripts
Tom Horton
Alfred C. Weaver
CS453 Electronic Commerce
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Overview
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HTML Forms
JavaScript and Forms
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Event model and events
CGI Programming for server-side scripts
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HTML Forms
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Provide GUI-like components in your page
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Inputs: buttons, textboxes, radio buttons,
selections
Output fields: text boxes etc.
Can send information to the server
Can be accessed by JavaScript code on the
client-side
Tutorial with on-line fiddling:
http://www.w3schools.com/html/html_forms.asp
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Basics of Forms
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A form element: <FORM>
Inside:
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<INPUT TYPE=“…”>
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<TEXTAREA>
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Used to define a large number of common inputs
Empty element (no end-tag </INPUT>
(Except the following…)
multiple lines of text
<SELECT>
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List of choices in pop-up or scrollable list
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Common Form Element
Attributes
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On the <FORM> tag
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NAME=“symbolic name”
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Used in JavaScript to reference form and what’s inside it
METHOD=“…” and ACTION=“…”
More on these later
On other tags:
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NAME=“symbolic-name”
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Required for almost all input tags (not buttons)
Used by JavaScript and when sending info to server
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<TEXTAREA>
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Use begin and end tags
Attributes:
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ROWS=“…” (four by default)
COLS=“…” (40 characters by default)
Default text
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What’s between <TEXTAREA> and
</TEXTAREA>
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<INPUT> types
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Specify with <INPUT TYPE=“…”>
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TEXT: line of text
PASSWORD: line of text that hides what’s typed
CHECKBOX: yes/no
RADIO: use >1 for mutually exclusive choice
SUBMIT: button that initiates processing
Other attributes needed for each of these
Don’t forget NAME=“…”
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Single Line of Text
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<INPUT TYPE=“TEXT” …>
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Attributes: NAME, optionally SIZE,
MAXLENGTH, VALUE
Default text defined by VALUE
Example:
<INPUT TYPE=“TEXT” NAME=“tfield1”
VALUE=“your name here”
SIZE=“30”>
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A Checkbox
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<INPUT TYPE=“CHECKBOX” …>
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Attributes: NAME, optionally CHECKED, VALUE
What’s is the value when it’s checked? VALUE
attribute specifies this
CHECKED: initially displays checked
Example:
<INPUT TYPE=“CHECKBOX” NAME=“cbox1”
VALUE=“cbox1on” CHECKED>
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Radio buttons
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<INPUT TYPE=“RADIO” …>
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Attributes: NAME, optionally CHECKED, VALUE
Mutually exclusive checkboxes
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None or one can be checked, not more than one
Use same NAME value to “group” a set of these!
Note: when retrieving these in JavaScript, you get back an
array of values
CHECKED if one checked by default
Example:
<INPUT TYPE=“RADIO” NAME=“rad1”
VALUE=“1st”> First choice
<INPUT TYPE=“RADIO” NAME=“rad1”
VALUE=“2nd”> Second choice
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Submit and Reset Buttons
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<INPUT TYPE=“SUBMIT” …>
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One of two button types
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TYPE=“RESET” clears all data in the form
Attributes: optionally VALUE, NAME
VALUE: name displayed, and what’s sent to the
server (more later). “Submit Query” is default
Example:
<INPUT TYPE=“RESET” VALUE=“Clear Form”>
<INPUT TYPE=“SUBMIT” VALUE=“Submit”>
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Aside: More General Buttons
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Also a <BUTTON> element that needs an
end-tag
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Text (or images) goes inside the element
Attributes: NAME, DISABLED, TYPE (push, reset,
submit), VALUE
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Submit buttton with image:
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Example that links to a page:
<button type="submit">
<img src="/images/icons/tick.png">Save</button>
<button type=”push”><a href=”reset.html">
<img src=”passkey.png”> Change Password
</a></button>
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Multiple Selections
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<SELECT> element with </SELECT>
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Need to organize this like a list,
so <INPUT> empty element not enough
Attributes: NAME, optionally SIZE,
MULTIPLE
Use <OPTION> for choices inside
<SELECT>
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Attributes: VALUE, optionally SELECTED
(for default)
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<SELECT> Examples
<select name="cars">
<option value="volvo">Volvo</option>
<option value="saab">Saab</option>
</select>
<select name=”lunch” MULTIPLE>
<option value=”pizza">Pizza</option>
<option value=”pasta">Pasta</option>
</select>
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Layout and Design Tips
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In HTML you don’t have full control over
layout
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Check for resizing, wrapping issues
Use line breaks <BR> and paragraphs <P>
Use lists <UL> or <DL> (descriptive lists)
Multiple forms in one page
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Each with a SUBMIT button
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And Then What Happens to that
Input?
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Again, two ways forms often used
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JavaScript functions process form data
Sent back to the server for processing
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No JavaScript involved
Something waiting on the back-end though
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JavaScript and Forms
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We have an event model that lets us:
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Associate an event-handler (JavaScript function)
with…
An event (e.g. value changed, got focus, hit
submit, etc.) that happens on…
A particular HTML element
E.g. <FORM … ONSUBMIT=“processForm()”>
See lists of events here:
http://www.w3schools.com/jsref/jsref_events.asp
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Some Nice Events
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ONCLICK
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Attach to particular element, or
<SCRIPT LANGUAGE=“JavaScript” etc.
FOR=“para” EVENT=“onclick”>
Note: in HTML/JavaScript code, probably better to
put event names in lower-case
Others:
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ONLOAD: when an element is loaded
Cursor tracking: ONMOUSEMOVE,
ONMOUSEOVER, ONMOUSEOUT
Input fields: ONFOCUS, ONBLUR (loses focus)
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<FORM> and Events
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Common to use ONSUBMIT to call function
when submit button sent
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And before FORM takes its ACTION (more on
ACTION soon, I promise)
<FORM … ONSUBMIT=“validateForm()”>
Method may:
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Validate fields by accessing form-input elements’
values
Use alert-boxes to confirm submission
Etc.
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More on ONSUBMIT
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If function specified with ONSUBMIT
returns true or false
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If true, form ACTION taken
If false, form ACTION not taken
In general, JavaScript function can
window.event.returnValue = false;
 Which cancels the default action of an
event on an element
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ACTIONs associated with
Forms
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Finally! The FORM element typically has
these attributes:
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ACTION points to a script (on the server) to
process form data values
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ACTION=“…” that points to a URL
METHOD=“…” with value GET or POST
Some special uses here
METHOD: usually POST
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More details later when we talk about CGI
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mailto: and ACTION
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mailto: -- special URL that pops up a
compose-email window in a browser
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If supported by your browser
Nice for testing in any case
Example:
<FORM
action="mailto:[email protected]"
method="post">
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Static Web Page Delivery
Web Server
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Author writes
HTML
Web server locates .htm file
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HTML stream returned to browser
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Browser processes
page
Client requests page
Client
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Client-side vs. Server-side
Processing
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Computer processing can happen in two
locations
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Server:
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Client:
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Accepts request, finds page, sends it
Gets HTML (or more?) from net, processes it,
displays it
Advanced things can happen on one or
both sides
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Many Technology Choices
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Client-Side Technologies:
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Scripting languages: JavaScript, VBScript
Java applets
XML
Server-Side Alternatives:
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CGI
Active Server Pages (ASP)
PHP
Java Server Pages (JSP)
ColdFusion
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Client-side Scripting
Languages
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What’s a Scripting Language?
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Not a full-scale programming language
Usually for a special purpose
Usually interpreted “on the fly”
Client-side scripting languages
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File contains script mixed in with HTML code
Sent from server to browser
Run “inside” the browser before HTML is displayed
Makes HTML pages dynamic, customized
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Dynamic Web Page Delivery
Web Server
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Author writes
instructions
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Web server locates instructions file
HTML and script are returned to browser
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Web browser processes script to
create HTML
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Client requests page
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Browser displays HTML
Client
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Server-side processing:
Overview
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Lots of processing can happen on the server before returning a
webpage to the client
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Run programs in a scripting language (e.g. ASP)
Manage sessions
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Cookies
Sessions, shopping baskets, log-ins, etc.
Database processing
But the following slide shows when this processing happens
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At Step 4!
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Server-side Dynamic Page
Delivery
Web Server
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Author writes
instructions
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Web server locates instructions file
Web server processes instructions to create HTML
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HTML stream returned to browser
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Browser processes
page
Client requests page
Client
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CGI Scripts
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When not using mailto:, what happens?
Simplest (oldest) approach:
CGI (Common Gateway Interface)
ACTION points to a script on the server
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That script can process form input values
It generates HTML that it writes which is then
displayed back in the browser
On-line:
http://hoohoo.ncsa.uiuc.edu/cgi/forms.html
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Scripts
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Scripts written in: UNIX Shell, perl, C,
etc.
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Perl and other scripting languages have
rich libraries to help
Scripts stored where?
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Depends on your webserver
Apache on UNIX: central location and peruser scripts
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GET vs POST
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If you used POST
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If you used GET
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Form data sent back with the URL defining the
script and you read it from standard-input
Form data sent back in a separate environment
variable accessible in the web-server
What this means: don’t care since…
Use a library call to grab values
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E.g. in Perl: cgi-lib.pl which provides a &ReadParse
function that creates a map (associative array)
with form name/value pairs
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CGI in Practice
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Lots of tips and tricks
Lots of how-to on the Web
And in our Virtual Labs
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Do the unit on perl
See information there on CGI
Download perl and Apache webserver
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Windows: http://www.wampserver.com/en/
Mac: MAMP
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