Create a random array of objects

I want to create a random array with different types, but I won't return the same type twice.

I have 6 class for example that inherited from another super class :

Here are the classes, lets say they are empty and contain nothing just for example:

class PrimaryClass {
}

class A extands PrimaryClass {
}
class B extands PrimaryClass {
}
class C extands PrimaryClass {
}
class D extands PrimaryClass {
}
class E extands PrimaryClass {
}
class F extands PrimaryClass {
}

I have a function randomObject() that returns a random object : (in the main.ts)

function getRandomobject() : PrimaryClass {
let randomNumber : number = Math.floor(Math.random() * (6)) + 1; // random num between 1-6
switch (randomNumber) {
case 1 : return new A();
case 2 : return new B();
case 3 : return new C();
case 4 : return new D();
case 5 : return new E();
case 6 : return new F();
}
}

Now , in the main.ts class I create an array with length 3 for example :

let arr : PrimaryClass [] = new Array <PrimaryClass>(3); 

I want to fill the array with random types ​​like :

• A , B , C
• B , D , E
• F , A , B

But don't repeat the same type twice.

I checked the type of objects I created:

let typeA: A = new A(); // Type of is object
let typeB: B = new B(); // Type of is object
let typeC: C = new C(); // Type of is object

I want to fill the array with simple loop :

for (let i = 0 ; i< arr.length ; i++) {
arr[i] =  getRandomobject();
}

So, all types are objects so how can I check that something is no longer created in the array?

I want to compare every object created from the function to existing objects already, but how do I check its type? (Check type A,B,C...)