$.fn.countTo = function (options) { options = options || {};//當options未被初始化，即typeof options = 'undefined'時，執行后面部分即var options = {}來初始化一個對象 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  //引用和變量每次更新將改變  var self = this,//返回html對象  $self = $(this),//返回返回一個jquery對象  loopCount = 0,  value = settings.from,  data = $self.data('countTo') || {};//獲取jauery方法對象  $self.data('countTo', data);//賦值  // if an existing interval can be found, clear it first  //如果存在間隔，則清除它  if (data.interval) {  clearInterval(data.interval);  }  data.interval = setInterval(updateTimer, settings.refreshInterval);  // initialize the element with the starting value  //用開始的值初始化  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); }