TypeScript typed array usage

Question

I have a TypeScript class definition that starts like this;

module Entities {          

    export class Person {
        private _name: string;
        pri         


        

Answer 1

You could try either of these. They are not giving me errors.

It is also the suggested method from typescript for array declaration.

By using the Array<Thing> it is making use of the generics in typescript. It is similar to asking for a List<T> in c# code.

// Declare with default value
private _possessions: Array<Thing> = new Array<Thing>();
// or
private _possessions: Array<Thing> = [];
// or -> prefered by ts-lint
private _possessions: Thing[] = [];

or

// declare
private _possessions: Array<Thing>;
// or -> preferd by ts-lint
private _possessions: Thing[];

constructor(){
    //assign
    this._possessions = new Array<Thing>();
    //or
    this._possessions = [];
}

Answer 2

You have an error in your syntax here:

this._possessions = new Thing[100]();

This doesn't create an "array of things". To create an array of things, you can simply use the array literal expression:

this._possessions = [];

Of the array constructor if you want to set the length:

this._possessions = new Array(100);

I have created a brief working example you can try in the playground.

module Entities {  

    class Thing {

    }        

    export class Person {
        private _name: string;
        private _possessions: Thing[];
        private _mostPrecious: Thing;

        constructor (name: string) {
            this._name = name;
            this._possessions = [];
            this._possessions.push(new Thing())
            this._possessions[100] = new Thing();
        }
    }
}

Answer 3

The translation is correct, the typing of the expression isn't. TypeScript is incorrectly typing the expression new Thing[100] as an array. It should be an error to index Thing, a constructor function, using the index operator. In C# this would allocate an array of 100 elements. In JavaScript this calls the value at index 100 of Thing as if was a constructor. Since that values is undefined it raises the error you mentioned. In JavaScript and TypeScript you want new Array(100) instead.

You should report this as a bug on CodePlex.