Is TypeScript really a superset of JavaScript re: functions?

Question

function foo(a: number, b: string): string {
    return a + b;
}

whether I put this in TypeScript playground or VS Code gets a 1068: Unexpected token. A constructor, method, accessor, or property was expected.

Once I make that into a standard TS method signature (by removing the function keyword), everything is fine.

Yet the latest documentation on TypeScript:

Shows function is totally usable. Very strange.

Works fine here when tring that exact snippet on typescriptlang.org/play — Jelle
– Jelle, Commented Jan 21, 2019 at 22:32
If you are inside a class then function is not allowed. But that hold true for es2015 classes as well.. — Titian Cernicova-Dragomir
– Titian Cernicova-Dragomir, Commented Jan 21, 2019 at 22:35
Yes, standalone function works, but within a class definition not. [link]typescriptlang.org/play/… — Alex. A
– Alex. A, Commented Jan 21, 2019 at 22:36
Yep, that is exactly how it works. Inside a class you don't use the function keyword and outside of it you need it. — Jelle
– Jelle, Commented Jan 21, 2019 at 22:40

basarat · Accepted Answer · 2019-01-21 23:02:19Z

2

This is an example that shows the error you are getting:

class Foo {
  // ERROR unexpected token
  function foo(a: number, b: string): string {
    return a + b;
  }
}

This is invalid TypeScript because, it is invalid JavaScript. e.g. the following is invalid:

answered Jan 21, 2019 at 23:02

basarat

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