Typescript error runtime error: Cannot read property 'prototype' of undefined when extending

Question

So I'm getting the above error in the console. It's caused by _super being undefined when it's passed to __extends (in the generated .js).

Here's some test code that can be used to reproduce the error:

//This is the entirety of the file Test.ts module Test {     export class Test1 {         public Name: string;         public Number: number;          constructor() {          }     } } 

Then in a separate file I have a class that inherits from that one:

/// <reference path="Test.ts" /> module Test {     export class Test2 extends Test1 {         constructor() {             super();         }     } } 

The <reference path... shouldn't be needed (and isn't), but I added it to see if it helped (it didn't).

The files are included in the correct order (Test.ts then Test2.ts) via BundleConfig (running with or without optimisations doesn't have any effect).

I am probably being a giant noob, but I haven't the slightest clue what I've messed up. All the other instances of this problem I've found online are from folks using the command line compiler to combine multiple Typescript files into one single file. I'm using the bundler to do that, but even when I don't combine them, I get the exact same issue.

Please help me, I'm at my wits end!

As requested, here's the compiled javascript: Test.js:

//This is the entirety of the file Test.ts var Test; (function (Test) {     var Test1 = (function () {         function Test1() {         }         return Test1;     })();     Test.Test1 = Test1; })(Test || (Test = {})); //# sourceMappingURL=Test.js.map 

Test2.js:

var __extends = this.__extends || function (d, b) {     for (var p in b) if (b.hasOwnProperty(p)) d[p] = b[p];     function __() { this.constructor = d; }     __.prototype = b.prototype;     d.prototype = new __(); }; /// <reference path="Test.ts" /> var Test; (function (Test) {     var Test2 = (function (_super) {         __extends(Test2, _super);         function Test2() {             _super.call(this);         }         return Test2;     })(Test.Test1);     Test.Test2 = Test2; })(Test || (Test = {})); //# sourceMappingURL=Test2.js.map 

Answer 1

Possible reasons this is happening:

1. Quadruple-check that BundleConfig is concatenating the files in the correct order. This is by far the most common cause of that error.
2. Verify you don't have any top-level export directives in Test.ts. This would cause the file to become an external module and Test1 would no longer be visible.

Failing that, you should post the emitted JavaScript to the question so we can diagnose what's causing the issue.