原文：http://purplebamboo.github.io/2015/03/16/javascript-component/

var Class = (function() {
  var _mix = function(r, s) {
    for (var p in s) {
      if (s.hasOwnProperty(p)) {
        r[p] = s[p]
      }
    }
  }

  var _extend = function() {

    //开关 用来使生成原型时,不调用真正的构成流程init
    this.initPrototype = true
    var prototype = new this()
    this.initPrototype = false

    var items = Array.prototype.slice.call(arguments) || []
    var item

    //支持混入多个属性，并且支持{}也支持 Function
    while (item = items.shift()) {
      _mix(prototype, item.prototype || item)
    }


    // 这边是返回的类，其实就是我们返回的子类
    function SubClass() {
      if (!SubClass.initPrototype && this.init)
        this.init.apply(this, arguments)//调用init真正的构造函数
    }

    // 赋值原型链，完成继承
    SubClass.prototype = prototype

    // 改变constructor引用
    SubClass.prototype.constructor = SubClass

    // 为子类也添加extend方法
    SubClass.extend = _extend

    return SubClass
  }
  //超级父类
  var Class = function() {}
  //为超级父类添加extend方法
  Class.extend = _extend

  return Class
})()

var TextCount = Class.extend({
  init:function(config){
    this.input = $(config.id);
    this._bind();
    this.render();
  },
  render:function() {
    var num = this._getNum();

    if ($('#J_input_count').length == 0) {
      this.input.after('<span id="J_input_count"></span>');
    };

    $('#J_input_count').html(num+'个字');

  },
  _getNum:function(){
    return this.input.val().length;
  },
  _bind:function(){
    var self = this;
    self.input.on('keyup',function(){
      self.render();
    });
  }
})

$(function() {
  new TextCount({
    id:"#J_input"
  });
})