$.fn.countTo = function (options) {

options = options || {};//当options未被初始化，即typeof options = 'undefined'时，执行后面部分即var options = {}来初始化一个对象

 

return $(this).each(function () {

 // set options for current element

 var settings = $.extend({}, $.fn.countTo.defaults, {

 from:  $(this).data('from'),

 to:  $(this).data('to'),

 speed:  $(this).data('speed'),

 refreshInterval: $(this).data('refresh-interval'),

 decimals: $(this).data('decimals')

 }, options);

 

 // how many times to update the value, and how much to increment the value on each update

 //更新值多少次，每次更新值多快

 var loops = Math.ceil(settings.speed / settings.refreshInterval),

 increment = (settings.to - settings.from) / loops;

 

 // references & variables that will change with each update

 //引用和变量每次更新将改变

 var self = this,//返回html对象

 $self = $(this),//返回返回一个jquery对象

 loopCount = 0,

 value = settings.from,

 data = $self.data('countTo') || {};//获取jauery方法对象

 

 $self.data('countTo', data);//赋值

 

 // if an existing interval can be found, clear it first

 //如果存在间隔，则清除它

 if (data.interval) {

 clearInterval(data.interval);

 }

 data.interval = setInterval(updateTimer, settings.refreshInterval);

 

 // initialize the element with the starting value

 //用开始的值初始化

 render(value);

 

 function updateTimer() {

 value += increment;

 loopCount++;

 

 render(value);

 

 if (typeof(settings.onUpdate) == 'function') {

  settings.onUpdate.call(self, value);

 }

 

 if (loopCount >= loops) {

  // remove the interval

  $self.removeData('countTo');

  clearInterval(data.interval);

  value = settings.to;

 

  if (typeof(settings.onComplete) == 'function') {

  settings.onComplete.call(self, value);

  }

 }

 }

 

 function render(value) {

 var formattedValue = settings.formatter.call(self, value, settings);

 $self.html(formattedValue);

 }

});

};

 

$.fn.countTo.defaults = {

from: 200,  // the number the element should start at

to: 0,   // the number the element should end at

speed: 1000,  // how long it should take to count between the target numbers

refreshInterval: 1, // how often the element should be updated

decimals: 0,  // the number of decimal places to show

formatter: formatter, // handler for formatting the value before rendering

onUpdate: null, // callback method for every time the element is updated

onComplete: null // callback method for when the element finishes updating

};

 

function formatter(value, settings) {

return value.toFixed(settings.decimals);

}

 

// custom formatting example

$('#count-number').data('countToOptions', {

formatter: function (value, options) {

return value.toFixed(options.decimals).replace(/\B(?=(?:\d{3})+(?!\d))/g, ',');

}

});

 

// start all the timers

$('.timer').each(count);

function count(options) {

var $this = $(this);

options = $.extend({}, options || {}, $this.data('countToOptions') || {});

$this.countTo(options);

}