Usage:

new CronJob('* * * * * *', function(){
    console.log('You will see this message every second');
});

Available Cron patterns:

Asterisk. E.g. *
Ranges. E.g. 1-3,5
Steps. E.g. */2

Read up on cron patterns here.

Another example:

new CronJob('00 30 11 * * 2-6', function(){
    // Runs every weekday (Monday through Friday)
    // at 11:30:00 AM. It does not run on Saturday
    // or Sunday.
});