Using namespacing assigning prototype object to anonymous function in object, this is undefined?

Question

I'm trying to assign a prototype inside a namespace using the following, (everything is wrapped in a global object):

prototypeObjects: {

        Person : function(config){

            var that = this;

            this.name = config.name;
            this.age = config.age;

            console.log(that);

            that.prototype.working = function(){

                console.log(this.name + 'is working');

            };

    },

},

I'm then using this in the console to check it:

var me = new global.prototypeObjects.Person({name:'Mike', age:'40'});

which gives this error:

TypeError: Cannot set property 'working' of undefined

However, if I am explicit in assigning the prototype, i.e.:

prototypeObjects: {

        Person : function(config){

            var that = this;

            this.name = config.name;
            this.age = config.age;

            console.log(that);

            **global.prototypeObjects.Person**.prototype.working = function(){

                console.log(this.name + 'is working');

            };

        }



    },

Then it works as expected and i get the following:

global.prototypeObjects.Person {name: "Mike", age: "40", working: function}

and me.working() logs out 'Mike is working'

Can somebody explain why I can't use 'this' in this instance?

Community · Accepted Answer · 2017-05-23 10:25:31Z

1

You define the prototype function in the constructor's body, you should define the prototype functions outside the function body:

var global={};
global.pototypeObjects= {
   Person : function(config){
     this.name = config.name;
     this.age = config.age;
   }
};
global.pototypeObjects.Person.prototype.working=function(){
  console.log(this.name + " is working");
};
var p = new global.pototypeObjects.Person(
  {name:"jon",age:22}
);
p.working();//jon is working

Here is some basic explanation about prototype and setting up inheritance: Prototypical inheritance - writing up

It's better not to use var in constructor functions as they will create closures and these objects take more cpu to initialize and more memory.

edited May 23, 2017 at 10:25

CommunityBot

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answered Jul 2, 2013 at 0:12

HMR

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5 Comments

Michael Snow Over a year ago

Marked as correct for the detail and the external link. Working perfectly now, Thank-you sir!

RobG Over a year ago

+1 but using "var" in a constructor has nothing to do with whether closures are created or not. Closures are a consequence of creating functions that persist beyond the life of their enclosing scope.

HMR Over a year ago

@RobG A closure is the return value of a function that has an environment associated to it to accommodate for variables declared in the function with var not going out of scope when the function returns. If I have var name = "" in person and create a new person() then what's returned is a closure because an environment is associated with person to make name available.

HMR Over a year ago

@RobG Sorry, you are correct, closures are created when defining functions in the constructor's body. This is usually the case when you want to use "private" variables defined with var because these are not available in prototype functions (outside the constructors body). But when defining a variable with var in the body and using it right there should not create closures.

RobG Over a year ago

@HMR—yes. Also, formal parameters create local variables as if by use of "var". Strictly, any "inner" function has a reference to the entire outer function's scope chain and hence creates the environment for a closure to be created. Whether one is or not depends on the persistence of the inner function. :-)

kalley · Accepted Answer · 2013-07-02 00:06:14Z

0

Because you've already instantiated the object. prototype exists on the class, not the object. You could just do:

this.working = function() {}

Otherwise, you should move it outside the constructor.

answered Jul 2, 2013 at 0:06

kalley

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1 Comment

HMR Over a year ago

Why would you declare a function in the constructor's body? The function does the same for each instance of person so should and can be shared but this way every person instance has it's own working function that will take extra cpu to initialise and more memory to store.

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