Uncaught SyntaxError: Unexpected number...?

var questions = [
  ['Which fictional city is the home of Batman?', 'Gotham City'],
  ['In which sport would you perform the Fosbury Flop?', 'The high jump.'],
  ['Spinach is high in which mineral?', 'Iron'],
  ['What is a Geiger Counter used to detect?', 'Radiation']
]

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

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

for ( var i = 0, 1 < questions.length; i =+ 1 ) {
  question = questions[i][0];
  answer = questions[i][1];
  response = str.toLowerCase(prompt(question));
  if ( response === answer) {
    correctAnswer += 1;
  }
}

html = "You got " + correctAnswer + "questions right!";
print(html);

var questions = [
  ['Which fictional city is the home of Batman?', 'Gotham City'],
  ['In which sport would you perform the Fosbury Flop?', 'High jump'],
  ['Spinach is high in which mineral?', 'Iron'],
  ['What is a Geiger Counter used to detect?', 'Radiation']
]

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

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

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

html = "You got " + correctAnswer + " questions right!";
print(html);