Cookies and JavaScript

1
Cookies and JavaScript

• How to make your page really cook!

2
Problem Can my page remember things?

• The WEB server has no way of tracking whether or
  not it has seen you before, since each request is
  independent of previous requests. It has no way
  of remembering that you were there.

3
Cookies

• A COOKY is a file that resides on your hard drive
  and can be updated via HTML and queried via Java
  or Javascript
• This allows your web site to store information
  about users in their cookie files, rather than
  devoting server storage to it.
• For example, what happens if you store your
  homepage at NETSCAPE?

4
NETSCAPE HOME PAGES

• Netscape allows user to build and store their own
  customized home pages.
• Actually, all of the changeable material is not
  stored at NETSCAPE, but is just stored in the
  users cookie file.
• A Javascript program is downloaded to the users
  and then dynamically generates their home page.
  The user can save it if they wish.

5
LOGIC

• Javascript program checks to see if a homepage
  is already stored in your cookie file
• If not, it queries the user and lets them choose
  different layouts and content.
• All of this is stored back in their cookie file.
• The next time they go to netscape.com/custom
  their homepage is displayed.

6
The trick ...

• All that is ever at Netscape is a Javascript
  program
• Every user gets a different page when they point
  to http//www.netscape.com/custom
• Netscape can support an infinite number of users
  with one homepage.

7
Hmmm What are the limitations

• Cookie file is on a machine, so all users from
  the same machine get the same homepage (wont
  work in the labs)
• How do we fix this?
• Name the homepages? that allows multiple users on
  the same machine but
• Store cookie file on H drive? maybe..

8
Look at the source at Netscape
9
How do we use Cookie files in Marketing?

• Store customer characteristics in cookie file
• Adapt site behavior based on these
  characteristics
• Update Cookie file with new info as customer
  changes behavior

10
How do we query Cookie file?

• Need to reference the Cookie variable in Java or
  Javascript
• Code will dynamically decide what to display
  based on Cookie values
• For instance, query a database back on server for
  all products that match cookie specs

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• function getCookie(name)
• var cookie " " document.cookie
• var search " " name ""
• var setStr null
• var offset 0
• var end 0
• if (cookie.length gt 0)
• offset cookie.indexOf(search)
• if (offset ! -1)
• offset search.length
• end cookie.indexOf("",
  offset)
• if (end -1)
• end
  cookie.length
• setStr
  unescape(cookie.substring(offset,
• end))
• return(setStr)

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Reading Cookie with GetCookie

• The results are directed into variables in your
  routine
• To retrieve the value of cookie foo,
• Insert the getcookie function in your code and
  then the following Javascript line will get the
  value of the cookie..
• myVar GetCookie("foo")

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Other Techniques

• JAVA Applet
• Dynamic HTML
• CGI program with server data base

14
Find some examples

• Javascript - Netscape home page construction kit
• JAVA?
• CGI (most sites)

15
Conclusion

• Cookies, CGI and Javascript can be used together
  to maintain persistent information on the
  clients computer.
• Information could be list of entertainment
  channels, their userid and password to the site
  etc.
• Check out the cookies on your home computer.