在javascript中访问父对象

时间:2009-11-24 12:53:48

标签: javascript

    var user = {
        Name: "Some user",
        Methods: {
            ShowGreetings: function() {
                    // at this point i want to access variable "Name", 
                    //i dont want to use user.Name
                    // **please suggest me how??**
                 },
            GetUserName: function() { }
        }
    }

14 个答案:

答案 0 :(得分:56)

你不能。

JavaScript中没有向上的关系。

以例如:

var foo = {
    bar: [1,2,3]
}

var baz = {};
baz.bar = foo.bar;

单个数组对象现在有两个“父”。

你可以做的是:

var User = function User(name) {
    this.name = name;
};

User.prototype = {};
User.prototype.ShowGreetings = function () {
    alert(this.name);
};

var user = new User('For Example');
user.ShowGreetings();

答案 1 :(得分:22)

var user = {
    Name: "Some user",
    Methods: {
        ShowGreetings: function() {
            alert(this.Parent.Name); // "this" is the Methods object
        },
        GetUserName: function() { }
    },
    Init: function() {
        this.Methods.Parent = this; // it allows the Methods object to know who its Parent is
        delete this.Init; // if you don't need the Init method anymore after the you instanced the object you can remove it
        return this; // it gives back the object itself to instance it
    }
}.Init();

答案 2 :(得分:7)

Crockford

  

“特权方法可以访问私有变量和   方法,并且本身可以访问公共方法和   外“

例如:

function user(name) {
     var username = name;

     this.showGreetings = function()
     {
       alert(username);
     }  
}

答案 3 :(得分:4)

你可以尝试使用闭包的另一种方法:

function userFn(name){
    return {
        Methods: {
            ShowGreetings: function() {
                alert(name);
            }
        }
    }
}
var user = new userFn('some user');
user.Methods.ShowGreetings();

答案 4 :(得分:4)

正如其他人所说,使用普通对象,无法从嵌套子项中查找父项。

但是,如果您使用递归ES6 Proxies作为帮助者,则可能会这样做。

我编写了一个名为ObservableSlim的库,除其他外,它允许您从子对象遍历到父对象。

这是一个简单的例子(jsFiddle demo):

var test = {"hello":{"foo":{"bar":"world"}}};
var proxy = ObservableSlim.create(test, true, function() { return false });

function traverseUp(childObj) {
    console.log(JSON.stringify(childObj.__getParent())); // returns test.hello: {"foo":{"bar":"world"}}
    console.log(childObj.__getParent(2)); // attempts to traverse up two levels, returns undefined because test.hello does not have a parent object
};

traverseUp(proxy.hello.foo);

答案 5 :(得分:2)

大卫多尔沃德就在这里。最简单的解决方案是访问user.Name,因为user实际上是单身人士。

答案 6 :(得分:1)

晚会很晚,但这有效

var user = {
        Name: "Some user",
        Methods() {
              return {
                   that: this,
                   ShowGreetings: function() {
                      console.log(this.that.Name)
                    },
               GetUserName: function() { }
              }
       }
    }
user.Methods().ShowGreetings() // Some user

答案 7 :(得分:0)

这样怎么样?

user.Methods.ShowGreetings.call(user, args);

因此,您可以在ShowGreetings中访问user.Name

var user = {
    Name: "Some user",
    Methods: {
        ShowGreetings: function(arg) {
            console.log(arg, this.Name);
        },
        GetUserName: function() { }
    },
    Init: function() {
        this.Methods.ShowGreetings.call(this, 1);
    }
};

user.Init(); // => 1 "Some user"

答案 8 :(得分:0)

老问题,但为什么你不能做这样的事情:

var user = {
        Name: "Some user",
        Methods: {
            ShowGreetings: function() {
                    // at this point i want to access variable "Name", 
                    //i dont want to use user.Name
                    // **please suggest me how??**
                    var thisName = user.Name; //<<<<<<<<<
                 },
            GetUserName: function() { }
        }
    }

因为您只会在实例化用户后调用user.Methods.ShowGreetings()。因此,当您想要使用其名称时,您将了解变量'user'?

答案 9 :(得分:0)

作为一种变体:

var user = (obj => { 
    Object.keys(obj.Methods).map(option => {
        const currOpt = obj.Methods[option];
        if (currOpt instanceof Function) {
            obj.Methods[option] = currOpt.bind(obj);
        };
    });
    return obj;
})({
    Name: "Some user",
    Methods: {
        Greeting: function () { return this.Name },
        GetUserName: function() { console.log(this) }
    },
});

但是我不知道为什么有人可以使用这种奇怪的方法

答案 10 :(得分:0)

我知道我来晚了。 我写了这个简单的方法。假设您有:

{
subObj: {
    x:'hello_world';
}
}

然后,如果要从subObj引用更大的对象,则可以将其转换为函数,并利用this

var tmpVal=reference_to_subObj; //keep value of subObj safe
reference_to_subObj=function(){return this;}//this returns the scope, here the parent
var parent=reference_to_subObj(); //call the function
reference_to_subObj=tmpVal; delete tmpVal; //set things back to normal
//Now you have variable 'parent'.

我使用了Function()构造函数,因为它使我可以将函数创建为字符串,因此可以将字符串作为代码传递。

function findParent(stringReference) {
Function(/*same as above, except filled in all reference_to_subObj with stringReference.*/
//stringReference is a stringified version of dot or bracket notation.

所以我可以打电话给findParent('obj.subObj')

答案 11 :(得分:0)

就像@Quentin说的那样,JS中没有向上的关系。但是,请尝试这种解决方法;

foo = { bar: {parent: foo} };
console.log(foo);
console.log(foo.bar.parent);

也类似于;

function Foo(){
    this.bar = {parent: this}
}
foo = new Foo();
console.log(foo);
console.log(foo.bar.parent);

答案 12 :(得分:-1)

我遇到了这篇旧文章,试图记住如何解决问题。这是我使用的解决方案。它源自Harmes和Diaz的Pro JavaScript Design Patterns(Apress 2008)(第8页)。您需要声明一个函数,然后创建该函数的新实例,如下所示。注意Store方法可以访问“ this”。

function Test() {            
  this.x = 1;
}
Test.prototype = {
  Store: function (y) { this.x = y; },
}
var t1 = new Test();
var t2 = new Test();    
t1.Store(3);
t2.Store(5);    
console.log(t1);
console.log(t2);

答案 13 :(得分:-2)

// Make user global
window.user = {
    name: "Some user",
    methods: {
        showGreetings: function () {
            window.alert("Hello " + this.getUserName());
        },
        getUserName: function () {
            return this.getParent().name;
        }
    }
};
// Add some JavaScript magic
(function () {
    var makeClass = function (className) {
        createClass.call(this, className);
        for (key in this[className]) {
            if (typeof this[className][key] === "object") {
                makeClass.call(this[className], key);
            }
        }
    }
    var createClass = function (className) {
        // private
        var _parent = this;
        var _namespace = className;
        // public
        this[className] = this[className] || {};
        this[className].getType = function () {
            var o = this,
                ret = "";
            while (typeof o.getParent === "function") {
                ret = o.getNamespace() + (ret.length === 0 ? "" : ".") + ret;
                o = o.getParent();
            }
            return ret;
        };
        this[className].getParent = function () {
            return _parent;
        };
        this[className].getNamespace = function () {
            return _namespace;
        }
    };
    makeClass.call(window, "user");
})();

user.methods.showGreetings();