CODEWITHSUNDEEP
javascript
Victorino
Victorino

Reputation: 1641

Prototypes issue in javascript

i am just starting learn a prototypes in javascript an i can't understand what a problem is in my code. I'm sorry, my question may seem silly

i got an error like this : Uncaught TypeError: undefined is not a function

why is undefined? I inherited a function of the user. can't understand it :(

var user = {

    sayName: function() {
        console.log(this.name)
    }

  };

user.name = "viktor";

user.sayName();

var user2 = {};

user2.prototype = user;

user2.name = "segey";

user2.sayName();

Upvotes: 0

Views: 47

Answers (2)

Eugene Obrezkov
Eugene Obrezkov

Reputation: 2986

For you question correct solution will:

function User() {
    this.name = 'Viktor';
    return this;
}

User.prototype = Object.create({
    sayName: function() {
        return this.name;
    }
});

function User2() {}
User2.prototype = Object.create(User.prototype);

var user = new User();
user.sayName(); // 'Viktor'
user2 = new User2();
user2.name = 'Bogdan';
user2.sayName(); // 'Bogdan'

And detailed explanation with example. Let say we have some basic class Animal. Our Animal have age and name.

function Animal() {
    this.age = 5;
    this.name = "Stuffy";
    return this;
}

Animal.prototype = Object.create({
    getAge: function() {
        return this.age;
    },

    getName: function() {
        return this.name;
    }
});

And when I spent some time with architecture I understand that I also need SubClass of Animal. For example, let it will be Dog class with new property and functions. And also Dog must extend functions and properties from Animal class.

function Dog() {
    Animal.apply(this, arguments); // Call parent constructor
    this.wantsEat = true; // Add new properties
    return this;
}

Dog.prototype = Object.create(Animal.prototype); // Create object with Animal prototype
Object.extend(Dog.prototype, { // Any extend() function, wish you want
    constructor: Dog, // Restore constructor for Dog class
    eat: function() {
        this.wantsEat = false;
        return this;
    }
});

Or you can use Object.defineProperties() and extend in this way:

Dog.prototype = Object.create(Animal.prototype, {
    constructor: {
        value: Dog
    },

    eat: {
        value: function() {
            this.wantsEat = false;
            return this;
        }
    }
});

Upvotes: 1

elclanrs
elclanrs

Reputation: 94101

All you need to set up the prototype chain with plain objects is:

var user2 = Object.create(user); // set `user` as prototype of `user2`

user2.name = "segey";
user2.sayName();

Upvotes: 2

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