Main.as

package {
    import flash.display.Sprite;
    import flash.text.TextField;

    public class Main extends Sprite {
        public function Main() {
            var tf : TextField = new TextField();
            this.addChild(tf);
            var foo : Foo = new Foo("Alice", function (f : Function) : void {
                    tf.text = f(); // ok
                });
        }
    }
}

class Foo {
    public var name : String;
    public function Foo(name : String, callback : Function) {
        this.name = name;
        callback(this.bar);
    }

    private function bar() : String {
        return this.name;
    }
}

main.js

"use strict";

class Foo {
    constructor(name, callback) {
        this.name = name;
        callback(this.bar);
    }

    bar() {
        return this.name;
    }
}

let foo = new Foo("Alice", function (f) {
        console.log(f()); // error
    });