CODEWITHSUNDEEP
arraysclassobjecttypescript
VKR
VKR

Reputation: 685

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.

Upvotes: 39

Views: 126939

Answers (3)

fletchsod
fletchsod

Reputation: 3719

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.

Upvotes: 16

Serj Sagan
Serj Sagan

Reputation: 30208

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")
];

Upvotes: -1

basarat
basarat

Reputation: 275799

This is a very c# type of code:

var bks: Book[] = new Book[2];

In Javascript / Typescript you don't allocate memory up front like that, and that means something completely different. This is how you would do what you want to do:

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

Now to explain what new Book[2]; would mean. This would actually mean that call the new operator on the value of Book[2]. e.g.: 

Book[2] = function (){alert("hey");}
var foo = new Book[2]

and you should see hey. Try it

Upvotes: 68

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