I'm facing an issue with the following code. 

What it basically should do. It should load and parse a given JSON file. And in the RequestListender it should show the `ID` and the string `Hello` which is returned by the `ToString()` method in *Product.ts*. Where the `tProduct.Id` is shows up correctly, the `tProduct.ToString()` method fails with the error stated below.

Thanks a lot in advance.

*Error message:*

```
TypeError: tProduct.ToString is not a function. 
 (In 'tProduct.ToString()', 'tProduct.ToString' is undefined)

```

*File: Test.ts*

```
var currentProduct = null as pvis.Product;

function runTest(path) {
    var request = new XMLHttpRequest();
    request.onload = loadRequestListener;
    request.open("get", path, true);
    request.send();
}

function loadRequestListener () {
    var tProduct : pvis.Product = JSON.parse(this.responseText);
    if (tProduct.Id) {
        currentProduct = tProduct;
        alert('loaded with Id: ' + tProduct.Id );   
        alert('loaded with Content: ' + tProduct.ToString() );  
    }
    else {
        alert('product failed to load');
    }

}

```

*File Product.ts*

```
module pvis {
    export class Product {

        Id: string;

        ToString():string {
            return 'Hello';
        }
    }
}

```

*The HTML part:*

```
<body onload="runTest('assets/products/json/A379N.json')">

```

*The compiled Javascript:*

```
var pvis;
(function (pvis) {
    var Product = (function () {
        function Product() {
        }
        Product.prototype.ToString = function () {
            return 'Hello';
        };
        return Product;
    })();
    pvis.Product = Product;
})(pvis || (pvis = {}));
var currentProduct = null;
function runTest(path) {
    var request = new XMLHttpRequest();
    request.onload = loadRequestListener;
    request.open("get", path, true);
    request.send();
}
function loadRequestListener() {
    var tProduct = JSON.parse(this.responseText);
    if (tProduct.Id) {
        currentProduct = tProduct;
        alert('loaded with Id: ' + tProduct.Id);
        alert('loaded with Content: ' + tProduct.ToString());
    }
    else {
        alert('product failed to load');
    }
}

```

*The tsconfig.json (I'm not sure if it is relevant):* 

```
{
    "compilerOptions": {
        "target": "ES5",
        "removeComments": true,
        "preserveConstEnums": true,
        "out": "js/main.js",
        "sourceMap": true
    },
    "files": [
       "src/Test.ts"
    ]
}

```