Why am I receiving 'Unexpected token +=' in the console?

var correct += 1;

/*
Challenge Instructions

Ask at least five questions

Keep track of the number of questions the user answered correctly

Provide a final message after the quiz letting the user know the number of questions he or she got right.

Rank the player. If the player answered all five correctly, give that player the gold crown: 3-4 is a silver crown; 1-2 correct answers is a bronze crown and 0 correct is no crown at all.
*/

var correct = 0;


var answer1 = prompt ('What is your name?');
if (answer1.toUpperCase() === 'SPEIR') {
  var correct += 1;
}

var answer2 = prompt ('What is 2+2?');
if (answer2.toUpperCase() === 4 ) {
  var correct += 1;
}

var answer3 = prompt ('What is' + answer2 + ' + 2?');
if (answer3.toUpperCase() === 6 ) {
  var correct += 1;
}

var answer4 = prompt ('What is' + answer3 + ' + 2?');
if (answer4.toUpperCase() === 8 ) {
  var correct += 1;
}

var answer5 = prompt ('What is' + answer4 + ' + 2?');
if (answer5.toUpperCase() === 10 ) {
  var correct += 1;
}


/*
OUTPUT RESULTS
*/
document.write ("<h1>Looks like you got " + correct + " out of 5 questions correct!");



/*
OUTPUT RANK
*/
if ( correct === 5) { 
  document.write ("<h1><strong>You recieved a Gold Crown!<strong></h1>");

} 

else if ( correct >= 3) {
  document.write ("<h1><strong>You recieved a Silver Crown!<strong></h1>");
} 

  else if ( correct >= 1) {
  document.write ("<h1><strong>You recieved a Bronze Crown!<strong></h1>");
  }

else ( correct >= 3) {
  document.write ("<h1><strong>No crown for you ... sorry!<strong></h1>");
}