在其函数中使用 JavaScript 自定义对象变量

Question

从未处理过对象，但现在编写自定义对象进行测试

function GraphicsObject(text) {
            var type = text;
            var map = new Object();
            alert("test");
        }

  GraphicsObject.prototype.setAttribute = function(key, val) {
            alert(type);   // ReferenceError: type is not defined
            this.map[key] = val; ReferenceError: map is not defined
   };

为什么会出现这些错误，为什么脚本不喜欢那种语法？

编辑

这就是我使用对象的方式

 var g1 = new GraphicsObject("text");

Answer 1

function GraphicsObject(text) {
            // type and map are private variables
            // var type = text;
            // var map = new Object();
            this.type = text;
            this.map = {}; // suggested by 
            alert("test");
        }

GraphicsObject.prototype.setAttribute = function(key, val) {
            alert(this.type);   
            this.map[key] = val; 
   };

Answer 2

出现问题是因为 GraphicsObject

var type
var map

是私有变量，不能从外部访问，即使你扩展它。

这里有两种解决方案：

function GraphicsObject(text) {
  this.type = text;
  this.map = {};
  alert("GraphicsObject");
}

GraphicsObject.prototype.setAttribute = function(key, val) {
  this.map[key] = val; 
  alert('Type is: '+this.type);
  alert('You\'re setting: '+key+' attribute with value: '+val);
};


var GO = new GraphicsObject('some text');
GO.setAttribute('a', 'b');

还有另一个解决方案：

function GraphicsObject(text) {
  var type = text;
  var attributes = {};
  
  this.setAttribute = function(key, val) {
    attributes[key] = val; 
    alert('Type is: '+type);
    alert('You\'re setting: '+key+' attribute with value: '+val);
  }
  
  // because variables are private You've to write getter method to return them
  this.getAttribute = function(key) {
    return attributes[key];
  }

  this.setType = function(value) {
    type = value;
  }

  this.getType = function() {
    return type;
  };
}


var GO = new GraphicsObject('some text');
GO.setAttribute('a', 'b');