TypeScript typed array usage

Question

I have a TypeScript class definition that starts like this;

module Entities {                export class Person {         private _name: string;         private _possessions: Thing[];         private _mostPrecious: Thing;          constructor (name: string) {             this._name = name;             this._possessions = new Thing[100];         } 

Looks like an array of type Thing does not get translated correctly to the corresponding Javascript array type. This is a snippet from the generated JavaScript:

function Person(name) {     this._name = name;     this._possessions = new Entities.Thing[100](); } 

Executing code containing a Person object, throw an exception when attempting to initialize the _possession field:

Error is "0x800a138f - Microsoft JScript runtime error: Unable to get value of the property '100': object is null or undefined".

If I change the type of _possession to any[] and initialize _possession with new Array() exception is not thrown. Did I miss something?

Answer 1

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();         }     } }