[arrays] Arrays in type script

I am finding difficulty declaring array in typescript and accessing it.

below is the code working for me

class Book {
    public BookId: number;
    public Title: string;
    public Author: string;
    public Price: number;
    public Description: string;
}

class dataservice {
    getproducts() {
        var bk = new Book();
        bk.Author = "vamsee";
        bk.BookId = 1;
        var bks: Book[] = [bk,bk];

        return bks.length;
    }
}

var ds = new dataservice();
var button = document.createElement('button');

button.onclick = function () {     
    alert(ds.getproducts().toString());
}

document.body.appendChild(button);

When I change my code as below it fails when trying to assign value to array item.

var bks: Book[] = new Book[2];
bks[0].Author = "vamsee";
bks[0].BookId = 1;
return bks.length;

For me to add object in a loop I have to do it the second way.

A cleaner way to do this:

class Book {
    public Title: string;
    public Price: number;
    public Description: string;

    constructor(public BookId: number, public Author: string){}
}

Then

var bks: Book[] = [
    new Book(1, "vamsee")
];

You can also do this as well (shorter cut) instead of having to do instance declaration. You do this in JSON instead.

class Book {
    public BookId: number;
    public Title: string;
    public Author: string;
    public Price: number;
    public Description: string;
}

var bks: Book[] = [];

 bks.push({BookId: 1, Title:"foo", Author:"foo", Price: 5, Description: "foo"});   //This is all done in JSON.