CODEWITHSUNDEEP
javascriptobjectprototypeundefined
Robstaa
Robstaa

Reputation: 95

JavaScript - Apply one method to many objects

I have heard about the prototype method to apply one function or variable to several objects. But it does not work for me somehow. I created many objects kind of like this:

var item = {
  a: {
    aa: "lalala",
    ab: 1,
    something: 3
  },
  b: {
    ba: "jfjb",
    bb: 2,
    something: 4
  }
}

But when I know use the prototype method

item.prototype.bob = 2;

it does not work and shows me the error

Cannot set property 'bob' of undefined"

Same for a method

item.prototype.bob = function() {
   100 - this.something;
   this.something++;
}

Do you know what I do wrong or is there a different method to apply the same variable or function to many objects?

Upvotes: 0

Views: 107

Answers (4)

meriton
meriton

Reputation: 70574

The classic way is

function Person(firstName, lastName) {
    this.firstName = firstName;
    this.lastName = lastName;
}

Person.prototype.greet = function() {
    console.log(this.firstName + " says hello");
}

var pete = new Person("Peter", "Pan");

pete.greet();

Note that the prototype attribute is on the constructor (the function object we invoke with new to construct the object), not the constructed object itself.

In ECMAScript 6, you'll be able to write this in a more compact way:

class Person {
    constructor(firstName, lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    greet() {
        console.log(this.firstName + " says hello");
    }
}

new Person("Peter", "Pan").greet();

Upvotes: 1

GolezTrol
GolezTrol

Reputation: 116140

You confuse classes with object instances. You just have an anonymous object. item is the instance, not the class.

In the snippet below, a class is declared (Item, with capital i), an instance is created (item), and the prototype of the class is modified. You will see then that you can set a property on the prototype and read it though the instance, if you like.

var Item = function() {
  a = {
    aa: "lalala",
    ab: 1,
    something: 3
  };
  b = {
    ba: "jfjb",
    bb: 2,
    something: 4
  };
}

var item = new Item();

Item.prototype.bob = 'x';

alert(item.bob);

Upvotes: 1

Geeky
Geeky

Reputation: 7496

Here your item is an object by itself,it does not has any constructor, so you cannot define or set on prototype.Your code throws error

To fix this, it has to be something like the below

function item(a,b){
   this.a=a;
   this.b=b;
}
function a(aa,ab,something){
   this.aa=aa;
   this.ab=ab;
   this.something=something
}
item.prototype.bob=2;
item.prototype.method1 = function() {
   100 - this.something;
   this.something++;
}

Hope this helps

Upvotes: 0

Thanasis1101
Thanasis1101

Reputation: 1680

The prototype property is called on the class name and not on the object name. So, if item is an object of class MyClass then you should write:

MyClass.prototype.bob = 2;

You can find more information on the links below:

Upvotes: 0

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