A simple timer implementation

Timer.js

// Simple stop watch implementation in JavaScript. Supports functions
// such as:
//
// > `start`, `reset`, `time`, `pause`, `unpause`
//
// See [this demo](https://tinker.io/6154e/3) for information
//

window.Timer = (function () {

  var Timer;


  //
  // A simple timer object

  Timer = function () {
    this.start();
    return this;
  };

  // Start the timer (again if it was paused before)
  Timer.prototype.start = function () {
    this.s = (+new Date);

    if (this.t) {
      this.s -= this.t;
      delete this.t;
    }

    return this.time();
  };

  // Returns current time reading since starting
  Timer.prototype.time = function () {
    if (this.t) {
      return this.t;
    }

    return (+new Date) - this.s;
  };

  // Restart the timer
  Timer.prototype.restart = function () {
    delete this.t;
    return this.start();
  };

  // Pause the timer
  Timer.prototype.pause = function () {
    this.t = this.time();
    return this.t;
  };

  // Unpause the timer
  Timer.prototype.unpause = Timer.prototype.start;

  // Is it paused?
  Timer.prototype.paused = function () {
    return this.t && this.t > 0;
  };

  return Timer;

}());

Timer.test.js

// Test
var timer = new Timer;
timer.start();

console.log(timer.time());
setTimeout(function () { console.log(timer.pause()); }, 1000);
setTimeout(function () { console.log(timer.time()); }, 1500);
setTimeout(function () { console.log(timer.unpause()); }, 2000);
setTimeout(function () { console.log(timer.time()); }, 2500);
setTimeout(function () { console.log(timer.time()); }, 2550);
setTimeout(function () { console.log(timer.restart()); }, 3000);
setTimeout(function () { console.log(timer.time()); }, 3500);
setTimeout(function () { console.log(timer.start()); }, 3500);
setTimeout(function () { console.log(timer.time()); }, 3550);

// 0
// 1000
// 1000
// 1000
// 1500
// 1550
// 0
// 0
// 0
// 50