access parent object in javascript

问题:

    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() { }
        }
    }

回答1:

You can't.

There is no upwards relationship in JavaScript.

Take for example:

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

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

The single array object now has two "parents".

What you could do is something like:

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();

回答2:

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();

回答3:

Crockford:

"A privileged method is able to access the private variables and methods, and is itself accessible to the public methods and the outside"

For example:

function user(name) {
     var username = name;

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

回答4:

You can try another approach using a closure:

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

回答5:

As others have said, with a plain object it is not possible to lookup a parent from a nested child.

However, it is possible if you employ recursive ES6 Proxies as helpers.

I've written a library called ObservableSlim that, among other things, allows you to traverse up from a child object to the parent.

Here's a simple example (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);

回答6:

David Dorward's right here. The easiest solution, tho, would be to access user.Name, since user is effectively a singleton.

回答7:

How about this way?

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

So you can access user.Name in ShowGreetings

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"

回答8:

Old question but why can't you just do something like this :

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() { }
        }
    }

Because you will only call user.Methods.ShowGreetings() after the user has been instantiated. So you will know about the variable 'user' when you want to use its name ?

回答9:

I ran across this old post trying to remember how to solve the problem. Here is the solution I used. This is derived from Pro JavaScript Design Patterns by Harmes and Diaz (Apress 2008) on page 8. You need to declare a function and then create a new instance of it as shown below. Notice the Store method can access "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);

回答10:

// 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();