my implementation of "the Sleep FN" in Javascript

sleep.js

var sleep = function(howManyMs){
    howManyMs += +new Date(); // add timestamp
    while (+new Date()<howManyMs){ ; } // just a NOOP
};

// console:
//   > console.log(+new Date(), "hello")
//   > sleep(4000);
//   > console.log(+new Date(), "world");

// result:
//   > hello 1417013576580
//   > world 1417013580580 <- exactly two seconds later 

Nice, why not use Date.now()?

Also, it's too bad that this will pin the CPU while sleeping.