step 1. show the cookie
alert(document.cookie); //no content
step 2. create a new session cookie
document.cookie="cookie1=the first cookie";
alert(document.cookie); //cookie1=the first cookie
step 3. create another session cookie
document.cookie="cookie2=another cookie";
alert(document.cookie); //cookie1=the first cookie; cookie2=another cookie"
step 4. update the first cookie value
document.cookie="cookie1=the first cookie updated";
alert(document.cookie); //cookie1=the first cookie updated; cookie2=another cookie"
step 5. close the browser and reopen the same page. all session cookie are gone
alert(document.cookie); //nothing