We can collect second from the date and time like this. Here is an example
var dt= new Date();
Here is the second part of your ( client ) computer date and time
We can also take Seconds part from any date variable.
var dt= new Date("Aug 15, 2013 13:52:45");
Output is here
Showing changing Seconds value
Here we are displaying the seconds value when the page loads. This value does not change on real time. So we will execute the code in every seconds to display the real changing seconds value. To execute the code repeatedly we will use setTimeout function which triggers in every 1000 mille seconds ( 1 second )