如何在JavaScript的全局范围内向内部函数原型添加函数？

Question

function A() {  
    this.B = function() {  
        var bla;
    };
}
A.B.prototype.foo = function() {console.log("Do whatever");};

I get this:

TypeError: Cannot read property 'prototype' of undefined

How to add a function to the prototype of B in this case?

Answer 1

There are a couple of mistakes in our code... here is how:

function A() {
   this.B = function() {
      var blah;
   };
}

a = new A();
a.B.prototype.foo = function()  {console.log("Do whatever")};

Your first issue was doing:

this.B() = function...

That's not valid code, since you were calling method B and assing it a function, you had to reference the attribute.

Your other mistake, was not instantiating an "A" object, the function by itself can't be used as an object, it can only be called. That's why when you had:

A.B.prototype

You recieved that error message.

I hope that clears things up a bit for you, let me know if you have more doubts.

Answer 2

You need to make the inner function accessible by adding it to the outer prototype, then you can add functions to the inner object by using Outer.prototype.Inner.prototype without the immediate need for an instance of the outer object.

function A() {this.a="a";}
A.prototype.B = function() {this.b="b";}
A.prototype.B.prototype.foo = function() {console.log("b is:"+this.b);}
var a=new A();
var b=new a.B();
b.foo();

Answer 3

B is a property of A , and can only be accessed from instances of A .

var aObj = new A;
aObj.B();

You cannot access AB without using an instance of A .

You could access aObj.B.prototype , and add methods to that.

aObj.B.prototype.foo = function(){
    return 'test';
};
var bar = new aObj.B;
console.log(bar.foo()); // 'test'

var bObj = new A;
var foobar = new bObj.B;
console.log(foobar.foo()); // `foo` is undefined