Ionic Quiz Snipped -> can't solve a bug

My First Ionic project, so I need some help;) -> I startet an ionic quiz, where the user gets a question, and has 4 possible answers to choose from where one is correct. When i start the quiz, it works most of the time: output e.g. "Your answer 1 was wrong" or "Your answer 3 was right" but just sometimes, it displays an error: e.g. "Your answer 3 was "... <- rest is missing -> I want someone to solve this bug + also improve the script, so if all questions have been answered, it should stop giving new answers and go to a new results-page.