You can work in JS (since ES6) exactly as in C# :

C# code :

class person{
   int id;
   string name;
   int age;
}
person myPerson = new person();
List<person> people = new List<person>();
people.add(myPerson);

JS code :

class Person
{
    constructor(id, name, age)
    {
        this.id = id;
        this.name = name;
        this.age = age;
    }
}

myPerson = new Person("p1", "Tom", 54); 
people = [];
people.push(myPerson);

Hope it helps ! :)

C# is a strongly typed language, that is, you can declare a variable to be an instance of an object (or a primitive type) and then the language will throw an error if you violate this. So, a collection like this

List<person> people = new List<person>();

makes sense in C#. However, Javascript is a weakly typed language, that is, you can define a variable to be an instance of a class, but you cannot declare it. So, if you do something like this:

var myVariable = new MyClass();

then you have instantiated MyClass in your definition, but you only declared myVariable to be a variable.

In Javascript you can use arrays or objects as collections. Example using array:

class Rectangle {
  constructor(height, width) {
    this.height = height;
    this.width = width;
  }
}

var myCollection = []; //creating the collection
myCollection.push(new Rectangle(2, 3)); //adding an element to a collection
myCollection.push(new Rectangle(3, 2)); //adding an element to a collection
myCollection.push(new Rectangle(4, 4)); //adding an element to a collection
myCollection.push(new Rectangle(10, 15)); //adding an element to a collection

for (let rectangle of myCollection) {
    console.log(`${rectangle.width} x ${rectangle.height}`);
}

Example using object

let myCollection = {
    'first': 'a',
    'second': 'b',
    'third': 'c'
}

myCollection.fourth = 'd';

for (let key in myCollection) console.log(`${key} is ${myCollection[key]}`);

In Javascript, class is a syntactic sugar for functions. Example:

function MyClass(foo, bar) {
    this.myFoo = foo;
    this.myBar = bar;
}

let obj = new MyClass('abc', 'def');

console.log(obj);