var CountUp = function(target, startVal, endVal, decimals, duration, options) {

    // make sure requestAnimationFrame and cancelAnimationFrame are defined
    // polyfill for browsers without native support
    // by Opera engineer Erik M枚ller
    var lastTime = 0;
    var vendors = ['webkit', 'moz', 'ms', 'o'];
    for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
        window.requestAnimationFrame = window[vendors[x]+'RequestAnimationFrame'];
        window.cancelAnimationFrame =
          window[vendors[x]+'CancelAnimationFrame'] || window[vendors[x]+'CancelRequestAnimationFrame'];
    }
    if (!window.requestAnimationFrame) {
        window.requestAnimationFrame = function(callback, element) {
            var currTime = new Date().getTime();
            var timeToCall = Math.max(0, 16 - (currTime - lastTime));
            var id = window.setTimeout(function() { callback(currTime + timeToCall); },
              timeToCall);
            lastTime = currTime + timeToCall;
            return id;
        };
    }
    if (!window.cancelAnimationFrame) {
        window.cancelAnimationFrame = function(id) {
            clearTimeout(id);
        };
    }

    var self = this;

     // default options
    self.options = {
        useEasing : true, // toggle easing
        useGrouping : true, // 1,000,000 vs 1000000
        separator : ',', // character to use as a separator
        decimal : '.', // character to use as a decimal
        easingFn: null, // optional custom easing closure function, default is Robert Penner's easeOutExpo
        formattingFn: null // optional custom formatting function, default is self.formatNumber below
    };
    // extend default options with passed options object
    for (var key in options) {
        if (options.hasOwnProperty(key)) {
            self.options[key] = options[key];
        }
    }
    if (self.options.separator === '') { self.options.useGrouping = false; }
    if (!self.options.prefix) self.options.prefix = '';
    if (!self.options.suffix) self.options.suffix = '';

    self.d = (typeof target === 'string') ? document.getElementById(target) : target;
    self.startVal = Number(startVal);
    self.endVal = Number(endVal);
    self.countDown = (self.startVal > self.endVal);
    self.frameVal = self.startVal;
    self.decimals = Math.max(0, decimals || 0);
    self.dec = Math.pow(10, self.decimals);
    self.duration = Number(duration) * 1000 || 2000;

    self.formatNumber = function(nStr) {
        nStr = nStr.toFixed(self.decimals);
        nStr += '';
        var x, x1, x2, rgx;
        x = nStr.split('.');
        x1 = x[0];
        x2 = x.length > 1 ? self.options.decimal + x[1] : '';
        rgx = /(\d+)(\d{3})/;
        if (self.options.useGrouping) {
            while (rgx.test(x1)) {
                x1 = x1.replace(rgx, '$1' + self.options.separator + '$2');
            }
        }
        return self.options.prefix + x1 + x2 + self.options.suffix;
    };
    // Robert Penner's easeOutExpo
    self.easeOutExpo = function(t, b, c, d) {
        return c * (-Math.pow(2, -10 * t / d) + 1) * 1024 / 1023 + b;
    };

    self.easingFn = self.options.easingFn ? self.options.easingFn : self.easeOutExpo;
    self.formattingFn = self.options.formattingFn ? self.options.formattingFn : self.formatNumber;

    self.version = function () { return '1.7.1'; };

    // Print value to target
    self.printValue = function(value) {
        var result = self.formattingFn(value);

        if (self.d.tagName === 'INPUT') {
            this.d.value = result;
        }
        else if (self.d.tagName === 'text' || self.d.tagName === 'tspan') {
            this.d.textContent = result;
        }
        else {
            this.d.innerHTML = result;
        }
    };

    self.count = function(timestamp) {

        if (!self.startTime) { self.startTime = timestamp; }

        self.timestamp = timestamp;
        var progress = timestamp - self.startTime;
        self.remaining = self.duration - progress;

        // to ease or not to ease
        if (self.options.useEasing) {
            if (self.countDown) {
                self.frameVal = self.startVal - self.easingFn(progress, 0, self.startVal - self.endVal, self.duration);
            } else {
                self.frameVal = self.easingFn(progress, self.startVal, self.endVal - self.startVal, self.duration);
            }
        } else {
            if (self.countDown) {
                self.frameVal = self.startVal - ((self.startVal - self.endVal) * (progress / self.duration));
            } else {
                self.frameVal = self.startVal + (self.endVal - self.startVal) * (progress / self.duration);
            }
        }

        // don't go past endVal since progress can exceed duration in the last frame
        if (self.countDown) {
            self.frameVal = (self.frameVal < self.endVal) ? self.endVal : self.frameVal;
        } else {
            self.frameVal = (self.frameVal > self.endVal) ? self.endVal : self.frameVal;
        }

        // decimal
        self.frameVal = Math.round(self.frameVal*self.dec)/self.dec;

        // format and print value
        self.printValue(self.frameVal);

        // whether to continue
        if (progress < self.duration) {
            self.rAF = requestAnimationFrame(self.count);
        } else {
            if (self.callback) { self.callback(); }
        }
    };
    // start your animation
    self.start = function(callback) {
        self.callback = callback;
        self.rAF = requestAnimationFrame(self.count);
        return false;
    };
    // toggles pause/resume animation
    self.pauseResume = function() {
        if (!self.paused) {
            self.paused = true;
            cancelAnimationFrame(self.rAF);
        } else {
            self.paused = false;
            delete self.startTime;
            self.duration = self.remaining;
            self.startVal = self.frameVal;
            requestAnimationFrame(self.count);
        }
    };
    // reset to startVal so animation can be run again
    self.reset = function() {
        self.paused = false;
        delete self.startTime;
        self.startVal = startVal;
        cancelAnimationFrame(self.rAF);
        self.printValue(self.startVal);
    };
    // pass a new endVal and start animation
    self.update = function (newEndVal) {
        cancelAnimationFrame(self.rAF);
        self.paused = false;
        delete self.startTime;
        self.startVal = self.frameVal;
        self.endVal = Number(newEndVal);
        self.countDown = (self.startVal > self.endVal);
        self.rAF = requestAnimationFrame(self.count);
    };

    // format startVal on initialization
    self.printValue(self.startVal);
};