emitter that emits modified sine waves

sinbox.js

var EventEmitter = require('events').EventEmitter

var sinner = SinBox()

setInterval( function () {
    sinner.setAmplitude(12)
}, 500)
setInterval( function () {
    sinner.setFrequency(40)
}, 500)


sinner.on('data', function (data) {
    console.log(data)
})

function SinBox () {
    var self = new EventEmitter()

    self.freq = 0 // should be between 200ms and 4 seconds?
    self.amp = 0  // should be between 0 and 1

    self.start = Date.now()
    self.switcher = 0

    self.setAmplitude = function (amp) {
        self.amp = amp
        self.switcher = !self.switcher
        if (self.switcher)
            self.computeSignal()
    }

    self.setFrequency = function (freq) {
        self.freq = freq
        self.switcher = !self.switcher
        if (self.switcher)
            self.computeSignal()
    }

    self.computeSignal = function () {
        var now = Date.now()
          , ts = (now - self.start) / 1000
        var x = new Date(now - 14400000).toISOString().replace(/T/, ' ').replace(/Z/, '');
        var y = self.amp * Math.sin(self.freq * ts)


        self.emit('data', {x:x, y:y} )
    }

    return self

}