javascript享元模式的定义和如何应用代码实例详解

var Upload = function(uploadType) {
  this.uploadType = uploadType;
}

/* 删除文件（内部状态） */
Upload.prototype.delFile = function(id) {
  uploadManger.setExternalState(id, this);  // 把当前id对应的外部状态都组装到共享对象中
  // 大于3000k提示
  if(this.fileSize < 3000) {
    return this.dom.parentNode.removeChild(this.dom);
  }
  if(window.confirm("确定要删除文件吗？" + this.fileName)) {
    return this.dom.parentNode.removeChild(this.dom);
  }
}

/** 工厂对象实例化 
 * 如果某种内部状态的共享对象已经被创建过，那么直接返回这个对象
 * 否则，创建一个新的对象
 */
var UploadFactory = (function() {
  var createdFlyWeightObjs = {};
  return {
    create: function(uploadType) {
      if(createdFlyWeightObjs[uploadType]) {
        return createdFlyWeightObjs[uploadType];
      }
      return createdFlyWeightObjs[uploadType] = new Upload(uploadType);
    }
  };
})();

/* 管理器封装外部状态 */
var uploadManger = (function() {
  var uploadDatabase = {};

  return {
    add: function(id, uploadType, fileName, fileSize) {
      var flyWeightObj = UploadFactory.create(uploadType);
      var dom = document.createElement(&#39;p&#39;);
      dom.innerHTML = "<span>文件名称：" + fileName + "，文件大小：" + fileSize +"</span>"
             + "<button class=&#39;delFile&#39;>删除</button>";

      dom.querySelector(".delFile").onclick = function() {
        flyWeightObj.delFile(id);
      };
      document.body.appendChild(dom);

      uploadDatabase[id] = {
        fileName: fileName,
        fileSize: fileSize,
        dom: dom
      };

      return flyWeightObj;
    },
    setExternalState: function(id, flyWeightObj) {
      var uploadData = uploadDatabase[id];
      for(var i in uploadData) {
        // 直接改变形参（新思路！！）
        flyWeightObj[i] = uploadData[i];
      }
    }
  };
})();

/*触发上传动作*/
var id = 0;
window.startUpload = function(uploadType, files) {
  for(var i=0,file; file = files[i++];) {
    var uploadObj = uploadManger.add(++id, uploadType, file.fileName, file.fileSize);
  }
};

/* 测试 */
startUpload("plugin", [
  {
    fileName: &#39;1.txt&#39;,
    fileSize: 1000
  },{
    fileName: &#39;2.txt&#39;,
    fileSize: 3000
  },{
    fileName: &#39;3.txt&#39;,
    fileSize: 5000
  }
]);
startUpload("flash", [
  {
    fileName: &#39;4.txt&#39;,
    fileSize: 1000
  },{
    fileName: &#39;5.txt&#39;,
    fileSize: 3000
  },{
    fileName: &#39;6.txt&#39;,
    fileSize: 5000
  }
]);