Classes

Question 1

What is public property?

Answer 1

Property which will be available in the instance of the class

class A {
    public test = 1
}

It’s equals:

class A {
    test = 1
}

But it’s better to explicitly show public properties

Question 2

What is private property?

Answer 2

Property which will be available only in the scope of particular class

class A {
private _test = 1

testSome() {
    console.log(this._test)
} }

Usually private properties started with _ preffix

Question 3

What is class implements?

Answer 3

interface ITest {
some: string
}

class A implements ITest {
some: string
}

Helps to type a class to allow it to have some required properties or methods from an interface

Question 4

What is protected property?

Answer 4

Property which will be available in particular class, or in child classes, but not in instances

class A {
protected a = 1
}

Question 5

What is static property?

Answer 5

This is a property which is exist only as a property of a class

class A {
static test = 1
}

console.log(A.test)

Question 6

What is abstract class?

Answer 6

This is a class which can’t create instance, and can be used only for inheritance

abstract class A {
test() {
console.log(123)
}
}

const b = new A() - !!! will throw an error !!!

Question 7

What is readonly property?

Answer 7

This property cannot be changed

class A {
readonly some: number
}

Question 8

What is decorators?

Answer 8

Is a function that is applied to a class, method, property, or parameter to change its behavior or add additional functionality.

Started with “@” symbol.

We can add unlimited amount of decorators.

Decorators are initialized from top to bottom. But executed from bottom to top