Classes

Question 1

Accessor properties are represented by what methods?

Answer 1

getter & setter

Question 2

In an object literal, getter and setter are denoted by?

Answer 2

get & set

Question 3

What does getter do?

Answer 3

Getter binds an object property to a function which is called when it’s looked up

Question 4

What does setter do?

Answer 4

Setter bind an object property to a function which is called when someone tries to set it

Question 5

What is the basic “class” syntax?

Answer 5

class MyClass {
constructor() {…};
method1() {…};
method2() {…};
}

Question 6

What do you need to use in order to create a new object in class with all the listed methods?

Answer 6

new MyClass()

Question 7

What happens inside “class” if you call the ‘new’

Answer 7

constructor() is automatically called inside “class” which means we can initialize the object there

Question 8

What do you put between class methods?

Answer 8

Nothing!

Question 9

Where does “class” store its methods? (e.g class MyClass())

Answer 9

In MyClass.prototype

Question 10

What type is class? More precisely?

Answer 10

Function, more precisely the constructor method

// class is a function
alert(typeof User); // function

// …or, more precisely, the constructor method
alert(User === User.prototype.constructor); // true

Question 11

What are the three differences between classes and constructors?

Answer 11

1. Function created by class is labelled by a special internal property [[IsClassConstructor]]
2. Class methods are non-enumerable
3. Classes always “use strict”

Question 12

What is a “class field”?

Answer 12

Syntax that allows you to add any property

Question 13

What is the difference between a “class field” and methods inside class? (e.g class User())

Answer 13

Class field are set on individual objects, not on User.prototype

Question 14

What are the two ways to bind inside class functions? (syntax)

Answer 14

1. Pass a wrapper-function such as
   setTimeout(function() {
   user.sayHi(); // Hello, John!
   }, 1000);
2. The class field “click” is created on a per-object basis, there’s a separate function for each Button object, with this inside it referencing that object. We can pass button.click around anywhere, and the value of this will always be correct.

class Button {
constructor(value) {
this.value = value;
}
click = () => {
alert(this.value);
}
}

let button = new Button(“hello”);

setTimeout(button.click, 1000); // hello

Question 15

What is an important difference between class declaration and function declaration?

Answer 15

To call function, it doesn’t matter whether the function has been written before or after but classes MUST be defined before they are constructed

Question 16

What are the cons of classes in JavaScript?

Answer 16

1. Bad for functional programming (which is using functions to their fullest extent). There’s a principle “composition over inheritance” but with classes there is “inheritance over composition”
2. Conceptually there are no classes in JS and they are not needed there