Ensure required instance variables are set

[matthewmueller]

TypeScript Version: 2.4.0

Code

class Greeter {
  greeting: {
    en: 'world!'
  } 
  constructor(message: string) {
 
  }
  greet() {
      return "Hello, " + this.greeting.en;
  }
}

let greeter = new Greeter("world");
greeter.greet()

Expected behavior:

It would complain that this.greeting.en has not been set in the constructor.

Actual behavior:

Runtime error 🙀

[RyanCavanaugh]

Duplicate of #8476

[matthewmueller]

@RyanCavanaugh ah there it is. sorry about that!