JS Error "Uncaught TypeError: Cannot read property '0' of undefined" - Someone please tell me what is incorrect.

Question

I'm working on the quiz challenge in Stage 2 of Loops, Arrays and Objects, and my code looks exactly like the example (unless I'm missing something). When I run the program, I get the error "Uncaught TypeError: Cannot read property '0' of undefined" in my console" on js line 18. I don't see anything wrong with line 18. Does anyone else?

var quiz = [
  ["What year is it?", 2015],
  ["How old are you?", 24],
  ["How many days are in February usually?", 28]
]

var question;
var answer;
var response;
var correctAnswers = 0;
var html;

function print(message) {
  document.write(message);
}

for (var i = 0; i <= quiz.length; i += 1) {
  question = quiz[i][0];
  answer = quiz[i][1];
  response = parseInt(prompt(question));
  if (answer === response) {
    correctAnswers += 1;
  }
}

html = "You got " + correctAnswers + " right.";
print(html);

Answer 1 · 2015-03-06T03:46:15Z

March 6, 2015 3:46am

In your for loop, it needs to be i < quiz.length.

There are 3 items in the quiz array, so the length is 3. However, since array index starts at 0, the final array index will always be one fewer than its length - in this case the last index being 2. Since there isn't a quiz[3], there is no [0] property for a non-existent item and that's why it's returning an error.

for (var i = 0; i < quiz.length; i += 1) {
               // ^ Here
  question = quiz[i][0];
  answer = quiz[i][1];
  response = parseInt(prompt(question));
  if (answer === response) {
    correctAnswers += 1;
  }
}

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Margaret Godowns

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JS Error "Uncaught TypeError: Cannot read property '0' of undefined" - Someone please tell me what is incorrect.

1 Answer

Colin Bell

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Margaret Godowns

Margaret Godowns