Issue in typescript with generics: Cannot read property 'prototype' of undefined

Question

I'm learning some typescript but I'm not entirely sure what the problem in my code is. I'm trying to implement an event system to make my domain observable (similar to what C# has with events) in a generic way and it compiles without a hitch. It even shows the correct type inference in intellisense (for sender?) when I register a handler. But when I try to run it I keep getting a "Uncaught TypeError: Cannot read property 'prototype' of undefined " in the __extends helper function. This is my code: ``` module Pathing.Domain { export interface IEventArgs { } export interface EventHandler { (sender?: S, e?: T): void } export class StdEvent extends EventDelegate { } export class EventDelegate { private handlers: EventHandler[] = []; public add(handler: EventHandler): void { this.handlers.push(handler); } public remove(handler: EventHandler): void { this.handlers = this.handlers.filter(h => h != handler); } public raise(...ar…

Accepted Answer

The base class `EventDelegate` needs to be defined before the derived class `StdEvent`

```
export class EventDelegate {

}

export class StdEvent extends EventDelegate {
}
```

It's conceivable that in a future version the TypeScript compiler would take care of this for you, but until then you are responsible for ordering the definitions correctly.

Issue in typescript with generics: Cannot read property 'prototype' of undefined

Solution

Problem