how can i use object literal pattern in place of constructor function

Question

I am trying to learn different object declaration type and inheritance. Here, first I declared an object named parent using an object constructor. Then, another object child is introduced which inherits all the properties from parent.

Parent object using constructor is:

function parent(){
  this.parent_last_name="khan";
  this.occupation="business";

}

Then a child object is declared and I make it inherit all the properties and methods from parent object using

child.prototype=new parent();

In the same example, I replaced the constructor type declaration and used object literal type declaration.

var parent={
  name: "khan",
  occupation: "business",
  ask: function(){
    alert("what do you do?");
  },
};

It is giving me an error that "parent is not a constructor".and it is not printing anything.

My question is : 1) Why is the object literal is not working with this particular example? When do I use object literal type and when do I use a constructor?

2)advantage of constructor over object literal

and 3)literal type object declaration can do what i want to do here?

WHOLE CODE

<html>

    <body>
        <script>
            function parent() {
                this.parent_last_name = "khan";
                this.occupation = "business";

            }
            parent.prototype.ask = function() {
                alert("what do you do?");
            }

            function child() {
                this.child_name = "mohsin";
                this.occupation = "student";
            }
            child.prototype = new parent();
            var lol = new child();
            document.write(lol.child_name + " " + lol.parent_last_name);
        </script>
    </body>

</html>

Browser: Firefox

[Working for me](http://jsfiddle.net/AstroCB/nvphL/) and [here](http://jsfiddle.net/AstroCB/nvphL/1/)'s the full code (which is also working). — AstroCB, May 29 '14 at 14:06
(edited the post) i am using firefox...will it work for this statement..document.write(lol.child_name+" "+lol.parent_last_name); — AL-zami, May 29 '14 at 14:09
JSFiddle doesn't let you use `document.write()` [for good reason](http://stackoverflow.com/questions/802854/why-is-document-write-considered-a-bad-practice). — AstroCB, May 29 '14 at 14:15
actually above statement not working on my browser .if i use constructor function it works fine.if i replace it with object literal type declaration it doesn't work anymore — AL-zami, May 29 '14 at 14:16
you used constructor in the fiddle.in my post i said constructor works fine.if i use object literal to declare "PARENT" it doesn't work!! — AL-zami, May 29 '14 at 14:20

Matías Fidemraizer · Accepted Answer · 2014-05-29T14:18:44.227

An object literal is just an instance of Object while a constructor function is an instance of Function which can become a constructor when new operator is used behind it (i.e. new SomeFunc()).

Remember that functions are JavaScript's first-citizen constructs. They can be either old-school procedural functions, object methods and also object constructors.

When to use object constructors? Easy: when you want to reuse the same object structure across same or other script files and you might need prototype chain (inheritance).

If you need an object to be passed as argument of some function call or something like that, object literals is the way to go.

Anyway, whenever you create a function (either constructor function or not), you've a prototype available to define members that will be part of any instance created with the whole function. Since ECMA-Script 5.x you can also use Object.create(...):

var A = function() {};
A.prototype.doX = function();

Object.create(A.prototype, {
    doY: {
        value: function() { }
    }
});

Object.create approach is also another way to get inheritance in JavaScript, since it creates an object where its prototype is the one provided as first parameter of the whole function.

About the error...

You can't use an object literal using new operator and this is why Web browsers (or ECMA-Script runtimes...) will throw an error, because an object literal is an instance of Object rather than being of Function.

thanks for detailed explanation..how this error can be fixed? — AL-zami, May 29 '14 at 14:18
@user3138436 I believe my answer should answer the whole question: you can't use `new` with object literals. You need to use an object instantiated from a constructor function. Thus, declare parent object with a function instead of an object literal. — Matías Fidemraizer, May 29 '14 at 14:20

how can i use object literal pattern in place of constructor function

1 Answers1

About the error...