Counter in M: S format, javascript

I started to play with the idea and got to a stopwatch like this:

var Cronometro = function (opcoes) {
    this.opcoes = opcoes || {};
    this.contador = null;
    this.tempo = 0;
    this.configurar = function () {
        this.mostrador = this.opcoes.mostrador || document.querySelector('.mostrador');
        this.iniciar = this.opcoes.iniciar || document.querySelector('.iniciar');
        this.pausar = this.opcoes.pausar || document.querySelector('.pausar');
        this.iniciar.addEventListener('click', this.contar.bind(this));
        this.pausar.addEventListener('click', this.parar.bind(this));
        this.accao = this.opcoes.callback || function () {
            alert('chegou aos dez minutos!');

        }
    }

    this.contar = function () {
        var self = this;
        this.contador = setInterval(function () {
            self.mostrar.call(self, self.tempo++);
        }, 1000);
    }
    this.parar = function () {
        clearInterval(this.contador);
        this.contador = null;
    }
    this.formatarNumeros = function (nr) {
        var str = nr + '';
        return str.length < 2 ? '0' + str : str;
    }
    this.mostrar = function (tempo) {
        var minutos = Math.floor(tempo / 60);
        var segundos = tempo % 60;
        this.mostrador.innerHTML = [minutos, segundos].map(this.formatarNumeros).join(':');
        if (tempo == 36000) {
            this.parar();
            this.tempo = 0;
            this.accao();
            this.contar();
        }
    }

    this.configurar();
    this.contar();
}

jsFiddle: link

It's a recyclable object that has some methods for the features it needs. I wrote in PT so I think most of it explains itself.

You can pass elements to the show / stop / start features , otherwise it has default values that will look for classes .

The part that may need explanation is:

this.contar = function () {
    var self = this;
    this.contador = setInterval(function () {
        self.mostrar.call(self, self.tempo++);
    }, 1000);
}

The setInterval will run in the global scope. This means that if you use this within this function it will point to window . So I used var self = this; to save the reference of my object and use self.mostrar.call(self to call this.mostrar() with this right.

Doing so, recyclable, I can have multiple counters at a time.

I made a small function that you can control the time. (JQuery is not necessary for script operation, I just used it to manipulate the textbox and the buttons).

var Clock = {
  minutosStop: 10, //pode "setar"o tempo usando "Clock.minutosStop = 5" para 5 min
  totalSegundos: 0,
  start: function() {
    var self = this;
    this.interval = setInterval(function() {
      self.totalSegundos += 1;
      self.min = Math.floor(self.totalSegundos / 60 % 60);
      self.seg = parseInt(self.totalSegundos % 60);
      if (typeof self.onChange === 'function')
        self.onChange();
      if (self.min == self.minutosStop)
        self.fire();
    }, 1000, self);
    return this;
  },
  toString : function() {
    return String("00" + this.min).slice(-2) + ":" + String("00" + this.seg).slice(-2);
  },
  onChange: null,
  funcaoFire: null,
  pause: function() {
    clearInterval(this.interval);
    delete this.interval;
    return this;
  },
  resume: function() {
    if (!this.interval) this.start();
    return this;
  },
  fire: function() {
    if (typeof this.funcaoFire === 'function')
      this.funcaoFire();
    this.pause();
    this.totalSegundos = 0;
    return this;
  }
};

Clock.start();
Clock.funcaoFire = function() {
  alert(Clock.toString());
}
Clock.onChange = function() {
  $("#contador").val(Clock.toString());
}

$('#pauseButton').click(function() {
  Clock.pause();
});
$('#resumeButton').click(function() {
  Clock.resume();
});
$('#fireButton').click(function() {
  Clock.fire();
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script><div><inputid="contador" value="00:00" />
</div>
<div>
  <input id="pauseButton" type="button" value="Pause">
  <input id="resumeButton" type="button" value="Resume">
  <input id="fireButton" type="button" value="Fire">
</div>