How do you use a function to create an Object with Javascript?

Question

Im doing a course in JavaScript. Im at the "Objects and classes" chapter, and I do not know how to solve some assignements in my homework. The first exercise is like this

function createCat(name,age){
//Create a new object with the property "name" and the value defined by the argument "name".
//Add a new property to the object with the name "age" and use the value defined by the argument"age"
//Add a methos (function) called meow that returns the string "Meow"!
}

And this is what im trying

 function createCat(name,age){
      var Cat={};
        Cat.Name=name;
        Cat.Age=age;
        Cat.meow=function(){return "Meow!"};
        return Cat;
     }

Im testing the function loading the script in an index.html file, opening that file in a browser and then testing the functions in the web Console. I run the function and there is no problem. Then, I test if the Cat object was returned by writing Cat.Name in the console, which results in an error. The same thing happens when I call the function in a line of code below and then try to access the properties of the Object. The error reads "ReferenceError: Cat is not defined". What am I doing wrong? Thanks!

Kokodoko · Accepted Answer · 2020-11-02 19:43:36Z

5

A cleaner way to do this is to leave out the let Cat = {} part entirely. You can use the function itself to create a Cat object.

function Cat(name, age) {
    this.name = name;
    this.age = age;
    this.meow = () => console.log("Meow!");
}

let myCat = new Cat("Waldorf", 16)
let anotherCat = new Cat("Statler", 12)

myCat.meow()
console.log(anotherCat.name)

answered Nov 2, 2020 at 19:43

Kokodoko

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1 Comment

Wais Kamal Over a year ago

I agree this is a better answer.

Bulent · Accepted Answer · 2020-11-02 18:56:36Z

2

Your function returns Cat, but this is only a name in function scope. In order to use that name out of the function, you need to do this:

function createCat(name, age) {
        var cat = {};
        cat.Name = name;
        cat.Age = age;
        cat.meow = () => "Meow!";
        return cat;
}

let Cat = createCat("mist", 16);

console.log(Cat)

answered Nov 2, 2020 at 18:56

Bulent

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Comments

Wais Kamal · Accepted Answer · 2020-11-02 18:46:17Z

1

You get this error because Cat is only defined within the scope of your function. To define Cat globally, use window.Cat instead of var Cat:

function createCat(name, age) {
  window.Cat = {};
  Cat.Name = name;
  Cat.Age = age;
  Cat.meow = function() {
    return "Meow!"
  };
  return Cat;
}

console.log(Cat.Name);

answered Nov 2, 2020 at 18:46

Wais Kamal

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3 Comments

Kokodoko Over a year ago

This answer is actually not correct, because now the function will overwrite the window.Cat every time the function is called...

Wais Kamal Over a year ago

This is the only way you would be able to call Cat outside of the function. It is not a requirement (as per the exercise requirements) but it is the main reason the OP is getting the error.

Kokodoko Over a year ago

The OP's function returns a cat, so it makes more sense to store that returned cat in a variable. For example: let cat = createCat("Jonesy", 10). That way the cat is available in the global scope AND you can have more than one different cat.

SaizFerri · Accepted Answer · 2020-11-02 18:54:39Z

1

If you want to get your Cat when you type on the console Cat.name you have to declare it globally like so:

function createCat(name, age) {
  return {
    name: name,
    age: age,
    meow: function() {
      return "Meow!"
    },
  };
}

window.Cat = createCat('name', 2);

Then you can access your Cat globally.

You could also assign the Cat to a variable on the browser console and access it through Cat.name like so:

const Cat = createCat('name', 2);

answered Nov 2, 2020 at 18:54

SaizFerri

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