How to create a timer in web page!!

Question

and it should start when user enter the login button and it should stop when user press the logout, the time duration should be recorded !!

Answer 1

int time;

var recorder = setInterval (function(){
time++;
},1000);

//to stop on logout.
clearInterval(recorder);

Answer 2

*setInterval" is used. It won't be that difficult, try searching it.

Answer 3

Save in your database or a flat file. When someone logs in, record the time (using time() function in PHP, outputs a time as UNIX format) and after logging out, record another time. The difference between these two numbers is your target (in seconds).