Accurate BPM timer

bpm.js

/**
 * This code is based off http://www.sitepoint.com/creating-accurate-timers-in-javascript/
 * This is my adaptation to make it work with bpm, using this you can create abstract timers that are based off other measures
 */

// bpm is the number of beats in a minute
var bpm = 128;

// stop is just a var to let you stop the loop from continuing manually
var stop = false;

var start = new Date().getTime(),
    time = 0,
    // step is calculating how many milliseconds per beat
    step = 60000 / bpm;

function beat() {
    /**
     * Do your action per beat here
     **/
     
    // time is incremented by step we use this to compare against the start time
    time += step;
    
    // the difference is based off the current time - start time - time expected
    // this allows us to get a millisecond different and adjust the timeout below to be accurate 
    var diff = (new Date().getTime() - start) - time;
    
    // this is where the stop variable comes in, we can manually inject 'stop = true;' into the console to stop the loop
    if (!stop) window.setTimeout(beat, (step - diff));
}

// we start the beat loop
window.setTimeout(beat, step);