Timer.js

"use strict";

; var Timer = (function () {
    var defineIntervalProperties = function (target, starter, ender) {
        Object.defineProperties(
            target,
            {
                'start': {
                    'get': starter
                },
                'end': {
                    'get': ender
                },
                'milliseconds': {
                    'get': function () {
                        return this.end - this.start;
                    }
                },
                'seconds': {
                    'get': function () {
                        return this.milliseconds / 1e3;
                    }
                },
                'minutes': {
                    'get': function () {
                        return this.seconds / 60;
                    }
                },
                'hours': {
                    'get': function () {
                        return this.minutes / 60;
                    }
                },
                'days': {
                    'get': function () {
                        return this.hours / 24;
                    }
                }
            }
        );

        // Make the object immutable.
        Object.seal(target);
    };

    var T = function (start) {
        if (!Number.isInteger(start)) {
            start = +new Date;
        }

        defineIntervalProperties(
            this,
            function () {
                return start;
            },
            function () {
                return +new Date;
            }
        );
    };

    T.prototype.diff = function (timer) {
        if (!(timer instanceof T)) {
            throw new Error('Invalid timer supplied');
        }

        return new this.Interval(this.start, timer.start);
    };

    T.prototype.Interval = function (start, end) {
        if (!Number.isInteger(start)) {
            start = +new Date;
        }

        if (!Number.isInteger(end)) {
            end = +new Date;
        }

        defineIntervalProperties(
            this,
            function () {
                return start;
            },
            function () {
                return end;
            }
        );
    };

    T.Countdown = function (d) {
        if (!(d instanceof Date)) {
            throw new Error('Invalid date supplied');
        }

        var timer = new T, end = +d;

        defineIntervalProperties(
            this,
            function () {
                return timer.end;
            },
            function () {
                return end;
            }
        );
    };

    return T;
}());