最近项目中需要出现动态数字的动画效果，去git上一搜，发现好多轻量级的js插件，由于项目用的jquery，就选择了Counter-Up.js（https://github.com/bfintal/Counter-Up）。
效果如下：
【插件：Counter-Up】JS实现自增数字动画效果-QUI-Notes
使用步骤：
1.下载引入Counter-Up.js，请先引入jquery，否则，哼哼！
2.指定元素使用插件

$('.counter').countUp();

或指定动画时间

$('.counter').counterUp({
    delay: 10, //延迟
    time: 1000  //时间
});

大功告成！是不是很简单的一个插件，不需要懂太多原理，直接就能用！更多的可以去git查看其文档。

这个插件的原理：
1.扩展jquery方法counterUp ；
2.设置默认的时间周期和时间延迟；
3.遍历指定元素，将内容转换为数字类型，然后根据时延和周期算每次加多少，循环改变元素的值！

源代码：

/*!
* jquery.counterup.js 1.0
*
* Copyright 2013, Benjamin Intal http://gambit.ph @bfintal
* Released under the GPL v2 License
*
* Date: Nov 26, 2013
*/
(function( $ ){
  "use strict";

  $.fn.counterUp = function( options ) {

    // Defaults
    var settings = $.extend({
        'time': 400,
        'delay': 10
    }, options);

    return this.each(function(){

        // Store the object
        var $this = $(this);
        var $settings = settings;

        var counterUpper = function() {
            var nums = [];
            var divisions = $settings.time / $settings.delay;
            var num = $this.text();
            var isComma = /[0-9]+,[0-9]+/.test(num);
            num = num.replace(/,/g, '');
            var isInt = /^[0-9]+$/.test(num);
            var isFloat = /^[0-9]+\.[0-9]+$/.test(num);
            var decimalPlaces = isFloat ? (num.split('.')[1] || []).length : 0;

            // Generate list of incremental numbers to display
            for (var i = divisions; i >= 1; i--) {

                // Preserve as int if input was int
                var newNum = parseInt(num / divisions * i);

                // Preserve float if input was float
                if (isFloat) {
                    newNum = parseFloat(num / divisions * i).toFixed(decimalPlaces);
                }

                // Preserve commas if input had commas
                if (isComma) {
                    while (/(\d+)(\d{3})/.test(newNum.toString())) {
                        newNum = newNum.toString().replace(/(\d+)(\d{3})/, '$1'+','+'$2');
                    }
                }

                nums.unshift(newNum);
            }

            $this.data('counterup-nums', nums);
            $this.text('0');

            // Updates the number until we're done
            var f = function() {
                $this.text($this.data('counterup-nums').shift());
                if ($this.data('counterup-nums').length) {
                    setTimeout($this.data('counterup-func'), $settings.delay);
                } else {
                    delete $this.data('counterup-nums');
                    $this.data('counterup-nums', null);
                    $this.data('counterup-func', null);
                }
            };
            $this.data('counterup-func', f);

            // Start the count up
            setTimeout($this.data('counterup-func'), $settings.delay);
        };

        // Perform counts when the element gets into view
        $this.waypoint(counterUpper, { offset: '100%', triggerOnce: true });
    });

  };

})( jQuery );