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Cookies

Cookies. A cookie is a small text file written to the client's computer. 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

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Cookies

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  1. Cookies A cookie is a small text file written to the client's computer • 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

  2. 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

  3. What's in a cookie • The cookie name and cookie value • A cookie's expiration data • Path to the page creating the cookie • Domain name of the server creating the cookie • Security parameter that can restrict access to it Create a cookiedocument.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]

  4. Make the cookie <html><head></head><body> <script type="text/javascript"> var expDate = new Date(); expDate.setMonth(expDate.getMonth() + 1); document.cookie = "greeting=Hello World;expires=“ + expDate.toGMTString(); </script><h1>Wrote the Cookie</h1></body></html> Read the cookie <html><head></head><body><h1>Read the Cookie</h1> <script type="text/javascript"> alert(document.cookie); </script></body></html> Example Make Cookie and Read Cookie

  5. 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?

  6. 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);

  7. 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.

  8. 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); Output using example on the previous slide: Name=Bill;address=1250 Siskiyou blvd;city=Ashland;state=OR;zip=97520

  9. Splitting Cookies in Pieces Question: What's in theCookies[3]? • 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 97520 theCookies[0] = name=bill theCookies[1] = address=1250 Siskiyou blvd theCookies[2] = city=Ashland

  10. 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

  11. 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.

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