在 JavaScript 中定义一个“嵌套”的 object 构造函数？

Question

Is it possible to define an object within another object? I'm thinking something like this:

function MyObj(name) {
    this.name = name;

    function EmbeddedObj(id) {
        this.id = id;
    }
}

And I could then create an EmbeddedObj like this:

var myEmbeddedObj = new MyObj.EmbeddedObj();

Meme for bonus points: Objectception: :o

Answer 1

Yes, and no.

function MyObj(name) {
    this.name = name;
}
MyObj.EmbeddedObj = function EmbeddedObj(id) {
    this.id = id;
}
new MyObj.EmbeddedObj(42);

Would run, but it might not yield the expected results for "embedded object" (see comment).

Note that in the case of new expr the expression is evaluated first so, in this case it creates a new object using the function-object evaluated from MyObject.EmbeddedObj as a constructor. (There is a silly rule with parenthesis in the expression, but that's another story.)

---

Now, if a "parent" and "child" relationship was desired, that could be done, using a more round-about method:

function Parent (name) {
   this.name = name;
   var parent = this; // for closure
   this.Child = function Child () {
      this.Parent = parent;
   }
}

// create new parent object
var parent = new Parent();       
// each new parent has a different Child constructor and
// any function-object can be used as a constructor
var child = new parent.Child();
// true: child is "bound" to parent
child.Parent === parent;

Answer 2

function MyObj(name) {
    this.name = name;
}

MyObj.EmbeddedObj = function(id) {
    this.id = id;
}

var myEmbeddedObj = new MyObj.EmbeddedObj();

Does that look like what you're after?

Answer 3

Here is example of nested constructor.

function cimdb(name,review,year) {

 function nestedConstructor(name,review,year) {
    this.name = name;
    this.review = review;
    this.year = year
};

    this.name = name;
    this[name] = new nestedConstructor(name,review,year);

}



  var lionking = new cimdb("The Lion King", "The lion King review ..", 2015);

---

I guess this is what you mean by nested object constructor.

Answer 4

The easiest way to nest other objects in a constructor is to create its field and then create a new object when invoking the constructor. Below is an example:

function Product(name, price, category, producer) {
    this.name = name;
    this.price = price;
    this.category = category;
    // nested constructor
    this.producer = producer;
}

function Producer(contributor, address) {
    this.contributor = contributor;
    this.address = address;
}

let prod1 = new Product("Milk", 2.5, "Dairy", new Producer("Nestle", "Warszawa"));