how to convert a string to a Unix timestamp in javascript?

You can initialise a Date object and call getTime() to get it in unix form. It comes out in milliseconds so you’ll need to divide by 1000 to get it in seconds.

(new Date("2013/09/05 15:34:00").getTime()/1000)

It may have decimal bits so wrapping it in Math.round would clean that.

Math.round(new Date("2013/09/05 15:34:00").getTime()/1000)