Javascript quiz - display choices in a random order using Array.prototype

Question

I want to randomize the order of the choices. I added a script that was supposed to shuffle the order of the choices but it failed to do so. Nothing displays when I debug the quiz.

Here's the code that I added:

function shuffle(array) {
  var currentIndex = array.length, temporaryValue, randomIndex;

  // While there remain elements to shuffle...
  while (0 !== currentIndex) {

    // Pick a remaining element...
    randomIndex = Math.floor(Math.random() * currentIndex);
    currentIndex -= 1;

    // And swap it with the current element.
    temporaryValue = array[currentIndex];
    array[currentIndex] = array[randomIndex];
    array[randomIndex] = temporaryValue;
  }

  return array;
}

Javascript Quiz:

 var quiz = [{
          "question": "What is the full form of IP?",
          "choices": ["Internet Provider", "Internet Port", "Internet Protocol" , "Other"],
          "correct": "Other"

        }, {
          "question": "Who is the founder of Microsoft?",
          "choices": ["Bill Gates", "Steve Jobs", "Steve Wozniak" , "Martin Shaba"],
          "correct": "Bill Gates"
        }, {
          "question": "What was your first dream?",
          "choices": ["8 bits", "64 bits", "1024 bits"],
          "correct": "8 bits"
        }, {
          "question": "The C programming language was developed by?",
          "choices": ["Brendan Eich", "Dennis Ritchie", "Guido van Rossum"],
          "correct": "Dennis Ritchie"
        }, {
          "question": "What does CC mean in emails?",
          "choices": ["Carbon Copy", "Creative Commons", "other"],
          "correct": "Carbon Copy"
        }];

Answer 1

Add a scramble function to Array.prototype :

 if (!("scramble" in Array.prototype)) { Object.defineProperty(Array.prototype, "scramble", { enumerable: false, value: function() { var o, i, ln = this.length; while (ln--) { i = Math.random() * (ln + 1) | 0; o = this[ln]; this[ln] = this[i]; this[i] = o; } return this; } }); } var quiz = [{ "question": "What is the full form of IP?", "choices": ["Internet Provider", "Internet Port", "Internet Protocol", "Other"], "correct": "Other" }]; quiz.forEach(q => q.choices.scramble()); console.log(quiz[0].choices); 

---

Originally I had suggested:

quiz.forEach(q => q.choices.sort(() => Math.random() - .5));

DanDavis pointed out that particular method didn't achieve a reasonable distribution.

Answer 2

If you wanted "Other" to remain as the last choice after the shuffle, you could accomplish that with this code:

 var quiz = [{ "question": "What is the full form of IP?", "choices": ["Internet Provider", "Internet Port", "Internet Protocol", "Other"], "correct": "Other" }, { "question": "Who is the founder of Microsoft?", "choices": ["Bill Gates", "Steve Jobs", "Steve Wozniak", "Martin Shaba"], "correct": "Bill Gates" }, { "question": "What was your first dream?", "choices": ["8 bits", "64 bits", "1024 bits"], "correct": "8 bits" }, { "question": "The C programming language was developed by?", "choices": ["Brendan Eich", "Dennis Ritchie", "Guido van Rossum"], "correct": "Dennis Ritchie" }, { "question": "What does CC mean in emails?", "choices": ["Carbon Copy", "Creative Commons", "Other"], "correct": "Carbon Copy" }]; function shuffle(array) { var temporaryValue, randomIndex; var currentIndex = array.length; // While there remain elements to shuffle... while (currentIndex > 1) { // Pick a remaining element... randomIndex = Math.floor(Math.random() * currentIndex); currentIndex -= 1; // And swap it with the current element. temporaryValue = array[currentIndex]; array[currentIndex] = array[randomIndex]; array[randomIndex] = temporaryValue; } return array; } quiz.forEach(function(question) { var otherIndex; var choices = question.choices; var lastIndex = choices.length - 1; shuffle(choices); otherIndex = choices.indexOf('Other'); if (otherIndex >= 0) { choices[otherIndex] = choices[lastIndex]; choices[lastIndex] = 'Other'; } console.log(choices); });