Arrow function in "showPrompt" promise throws error

Hi

I'm having problems to make following code work...

class GamePlay {
  constructor(game) {
    this.game = game;
  }
  
  activateGameButtons() {
    setTimeout(() => {
      // --- Set reset button watch
      setWatch( (e) => {
        // Check for long press...
        var isLong = (e.time-e.lastTime)>0.4;
        if (isLong) {
          closeApp();
        }
        else this.resetScorePrompt();
      }, BTN2, { repeat: true, debounce: 50, edge: "falling" });
    },100);
  }
  
  resetScorePrompt() {
    clearWatch();
    E.showPrompt("Reset the score\nto 0-0?").then( (reset) => {
      if (reset) {
        this.game.resetScore();
      }
      this.activateGameButtons();
    });
  }
}

After pressing BTN2 I get my prompt and when selecting "yes" or "no" I get the following error (full error in attachment):

Uncaught SyntaxError: Got => expected ',' at ....

Is there something wrong with my Javascript code ? To me it looks like arrow functions aren't supported in promises. Because in other places, arrow functions work fine. When using 'function (reset) {}' instead of '(reset) => {}' I can enter the function, but then I'm having trouble with the "this scope".
(I'm a Javascript noob, so it might just be wrong Javascript code I guess :-))

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