添加为属性时，如何访问具有另一个功能的功能？

Question

I need to call function b from c. I am using the following code and I receive an error. Could you tell me what is wrong here?

 var a = function() { this.b = function() { alert('b'); }; }; var c = function() { ab(); }; c(); 

Answer 1

You could create an instance of a with new operator .

 var a = function() { this.b = function() { alert('b'); }; }; var c = new a; cb(); 

Another way is to add a property to the function and call it without a new instance.

 var a = function() {}; ab = function() { alert('b'); }; var c = function() { ab(); }; c(); 

Answer 2

The b is not visible on the a which you used. To access it, you need to create an object of a , because you add the b to the this . It means that it will be visible on the object of the type a .

 var a = function() { this.b = function() { alert('b'); }; }; var c = function() { new a().b(); // on the object }; c(); 

Answer 3

Better to have b as prototype function instead of having it inside constructor, because each time you create a new object of a , new function instance of b will be created. With prototype only one function instance will be maintained across all object instances of a .

var a = function() {
};

a.prototype.b = function() {
    alert('b');
};

Now you can access b by creating new instance of a

(new a()).b();

Answer 4

You should check how the this keyword works in javascript. In your code, this in the a function is bounded to the global object --which is window in browsers, so:

  var a = function() {
  this.b = function() {
    alert('b');
    };
 };
 a();
 window.b(); //will do the alert

As other answers state, is possible to do what your trying to do just by creating an object with the a function, either with:

var a = function() {

  return {
      b : function(){
          alert('b');
      }
  }

};
a().b(); //alert

Or with the new keyword:

    var a = function() {

  this.b = function() {
    alert('b');
  };
};
var obj = new a();

obj.b();

However, is worth mention that you don't need to explicitly create an object to achieve this behavior. You can also set a b member, which is a function, bounded to the a function:

var a = function() {
    //some code
};


a.b = function() {
    alert('b');
};

a.b();//alert

Which is more the thing you were trying to do in your question. You can do this due to the fact that functions in javascript are executable objects --However, to return explicitly an object and use is better than attach members to functions, imho.

Answer 5

Your original function is a constructor function , so you need to use the 'new' keyword to create an instance before calling its member function, b.

 var A = function() { this.b = function() { alert('b'); }; }; var c = function() { var _ = new A(); _.b(); }; c(); 

Answer 6

var a = function() {
           this.b = function() {
           alert('b');
           };
           return this;
        };
var c = function() {
            a().b();
        };

c();