javascript - 保护闭包内的对象不被外部修改

Question

我创建了这个对象，以便能够在其中存储数据，它具有一定程度的保护。只要新数据通过验证，任何人都可以获取它，任何人都可以设置它。

MF.factory = new function(){
    var data = {
        SITE_URL: document.URL.replace(/(https?:\/\/.+?)\/.*/, '$1'),
        xhrSettings: {
            type: 'GET',
            error: function(){},
            response: function(){},
            max_upload_file_size: 8388608
        }
    }
    this.get = function(key){
        return data[key];
    }
    this.set = {
        xhrSettings: {
            type: function(type){if(type in {POST:0,GET:0,PUT:0}) data.xhrSettings.type = type;},
            error: function(func){if(typeof func === 'function') data.xhrSettings.error = func;},
            response: function(func){if(typeof func === 'function') data.xhrSettings.response = func;},
            max_upload_file_size: function(size){if(!isNaN(size)) data.xhrSettings.max_upload_file_size = size;}
        }
    }
};

例如，现在我可以获得SITE_URL，但我无法设置它。这就是我正在寻找的限制。我可以设置 xhrSettings.type，只要它是 POST、GET 或 PUT。

MF.factory.set.xhrSettings.type("DGD"); // No effect
MF.factory.set.xhrSettings.type("POST"); // data.xhrSettings.type = "POST"

但是如果我这样做

a = MF.factory.get('xhrSettings');
a.type = "DGD";
console.log(MF.factory.get('xhrSettings'));

我看到 data 中的对象发生了变化，这使我的整个概念变得毫无用处。我该如何解决这个问题？

Answer 1

这正是 Object.freeze() 是为了。

来自 MDN:

The Object.freeze() method freezes an object: that is, prevents new properties from being added to it; prevents existing properties from being removed; and prevents existing properties, or their enumerability, configurability, or writability, from being changed. In essence the object is made effectively immutable. The method returns the object being frozen.

注意:IE v8 及以下版本不支持 Object.freeze()。