无法读取未定义的属性“推”-打字稿

Question

When I try to add to an array in Typescript (wrapped in Ionic2) I get an error telling me the array is undefined even though I've declared it. I've tried declaring it using two different declarations and not found the problem. The two declarations I used are:

tracker: any[];

and

tracker: Array<any>;

The first time I try to add anything to the array and where I get the error is below. I wanted to include the whole function, just in case there was something in there that could be redefining what 'this' is:

// Answer Correctly
  answerQuestionCorrectly(answer) {
    let answerButton = <HTMLButtonElement>document.getElementById('answer-' + answer.AnswerId);
    answerButton.addEventListener('click', (event) => {
      // Increase the score
      this.currentScore = this.currentScore + this.countdown;
      // Set up quiz review
      var correct = answer.AnswerText;
      var qTrack = {no: this.questionNo, q: this.questionText, a: answer.AnswerText, c: correct}
      console.log(qTrack);
      this.tracker.push(qTrack);
      console.log(this.tracker);
      // Check for end of questions
      if (this.questionNo < this.noOfQuestions) {
        // Remove the old answers
        var parent = document.getElementById('answers');
        this.answers.forEach(element => {
          var button = <HTMLButtonElement>document.getElementById('answer-' + element.AnswerId);
          parent.removeChild(button);
        });
        // Re-init the timer
        this.timer.initTimer();
        // Load Next Question
        this.loadQuestion();
      } else {
        // End the Quiz
        this.endOfQuiz();
      }
    });
  }

Answer 1

Those declarations only specify the type of the variable — it also needs a value. Try something like

var tracker: any[] = [];

to initialise the variable to an empty array.

Answer 2

You have to initialize the array before you can push an object into it.

tracker: any[ ] = [ ];

Answer 3

您必须像这样初始化它：

tracker: Array<any>=[];