Javascript equivalent of php's strtotime()?

Yes, it is. And it is supported in all major browser:

var ts = Date.parse("date string");

The only difference is that this function returns milliseconds instead of seconds, so you need to divide the result by 1000.

Check what valid formats can JavaScript parse.

I found this article and tried the tutorial. Basically, you can use the date constructor to parse a date, then write get the seconds from the getTime() method

var d=new Date("October 13, 1975 11:13:00");
document.write(d.getTime() + " milliseconds since 1970/01/01");

Does this work?

Check out this implementation of PHP's strtotime() in JavaScript!

I found that it works identically to PHP for everything that I threw at it.

Update: this function as per version 1.0.2 can't handle this case: '2007:07:20 20:52:45' (Note the : separator for year and month)

Update 2018:

This is now available as an npm module! Simply npm install locutus and then in your source:

var strtotime = require('locutus/php/datetime/strtotime');