Cookies Purpose –Write information that lives after the browser exits –Keep track of form data submitted multiple times during a particular visit –Track user purchase and visit habits –Examples Log-in account and password so the information doesn't broadcast over the web Shopping cart information Personalized greeting when the user next visits a site A cookie is a small text file written to the client's computer

Security It would be a serious security hole if html documents with JavaScript had unlimited access to client-side disks Client User Solutions –Block cookies altogether –Restrict cookies to certain trusted sites –Manage those cookies that are present –Restrict cookies to single sessions –Purge all cookies from the system Browser solutions: –Restrict cookies to 2,000 to 4,000 characters –Enforce expiration dates Caution –Editing cookies is dangerous because it could cause the browser to fail at certain web-sites

What's in a cookie 1.The cookie name and cookie value 2.A cookie's expiration data 3.Path to the page creating the cookie 4.Domain name of the server creating the cookie 5.Security parameter that can restrict access to it Create a cookie document.cookie = "userName=John doe"; Cookie name is 'userName' Cookie value is 'John doe' The first '=' is an assignment to the cookie property in the document object Read a cookie Alert(document.cookie); Notes: The browser normally sets items 3, 4, and 5 Syntax: [name]=[values];expires=[date];secure; path=[path];domain=[domain]

Example Make the cookie var expDate = new Date(); expDate.setMonth(expDate.getMonth() + 1); document.cookie = "greeting=Hello World;expires=“ + expDate.toGMTString(); Wrote the Cookie Read the cookie Read the Cookie alert(document.cookie); Make Cookie and Read Cookie

Expiration Dates Browsers hold cookies in memory –When a browser exits, it writes all cookies to disk –Browsers don’t save cookies that don’t have expiration dates How to set a cookie with an expiration date Var theName = document.someForm.name.value; document.cookie = "user="+theName + ";expires=" + expDate.toGMTString(); We'll describe expDate on the next slide Question: What use are cookies without an expiration date?

Computing an expiration date Instructions to set an expiration date var expDate = new Date(); var thirtyDaysMillis = 30*24*60*60*1000; var future = expDate.getTime() + thirtyDaysMillis; expDate.setTime(future); A short cut with fewer variables var expDate = new Date() expDate.setTime(expDate.getTime() + 30*24*60*60*1000); expDate.setTime(future); Another way to do it var expDate = new Date(); expDate.setMonth(expDate.getMonth() + 1);

Writing Multiple Cookies Just store over the cookie property more than once Each store creates a new cookie Example –document.cookie = "name=Bill"; –document.cookie = "address=1250 Siskiyou blvd"; –document.cookie = "city=Ashland"; –document.cookie = "state=OR"; –document.cookie = "zip=97520"; Note: This creates five cookies.

Reading Multiple Cookies We get all cookies at once What does JavaScript see? –Cookie names and values –Does NOT see expiration dates and security information Example –alert(document.cookie); Name=Bill;address=1250 Siskiyou blvd;city=Ashland;state=OR;zip=97520 Output using example on the previous slide:

Splitting Cookies in Pieces The split function does it! Assume the cookies are: Name=bill;address=1250 Siskiyou blvd;city=Ashland;state=OR;zip=97520 Here is the code var cookies = document.cookie; var theCookies = cookies.split(";"); alert(theCookies[0].split("=")[1]); alert(theCookies[1].split("=")[1]); alert(theCookies[2].split("=")[1]); alert(theCookies[3].split("=")[1]); alert(theCookies[4].split("=")[1]); Bill 1250 Siskiyou blvd Ashland OR theCookies[0] = name=bill theCookies[1] = address=1250 Siskiyou blvd theCookies[2] = city=Ashland Question: What's in theCookies[3]?

Server Side Programming Server side processing: starts where JavaScript leaves off Advantages –Different browsers don't execute the script differently –There is only one server, not millions of browsers to worry about Examples of server side languages –Php, perl, and Java servelets Capabilities –Create web pages that respond to user queries –Access databases and files stored on the server –Perform statistical analysis –Process forms –Many other features

Review Questions What is a cookie? What are three uses for cookies? How does a cookie get an expiration data? What does the split function do? Which cookies do browsers write to disk? When? Give an example of a limitation of JavaScript.