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JavaScript JavaScript Loops, Arrays and Objects Tracking Multiple Items with Arrays Build a Quiz Challenge, Part 2 Solution

Darien Kim
Darien Kim
3,126 Points
Posted by Darien Kim
Darien Kim
3,126 Points

can anyone explain, why ListHTML += "</ol>" why not = "<ol>" Thanks

can anyone explain, why ListHTML += "</ol>" why not = "<ol>" Thanks

and why does it have to add [] for variations? var correct = []; var wrong = [];

also my code has undefined on top , I cant find why it does that.

here is my code

var questions = [ ['How many states are in the United States?', 50], ['How many continents are there?', 7], ['How many legs does an insect have?', 6] ]; var correctAnswers = 0; var question; var answer; var response; var correct = []; var wrong = []; var html;

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

function buildList(arr) { var listHTML = "<ol>"; for (var i = 0; i < arr.length; i += 1) { listHTML += "<li>" + arr[i] + "</li>"; } listHTML += "</ol>"; return listHTML; }

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

if (response === answer) {

correct.push(question);

} else { wrong.push(question); } }

html += "<h2>you got these question right</h2>"; html += buildList(correct); html += "<h2>you got these questions wrong</h2>" html += buildList(wrong);

print(html);

Felix Sonnenholzer
Felix Sonnenholzer
14,654 Points
Felix Sonnenholzer
Felix Sonnenholzer
14,654 Points

Could you attach a snapshot of your workspace please?

2 Answers

Tom Sager
Tom Sager
18,987 Points
Tom Sager
Tom Sager
18,987 Points

ListHTML = "abc" sets the value of ListHTML to "abc". ListHTML += "def" takes the existing value of ListHTML and appends the string to the end. It is a shorthand for ListHTML = ListHTML + "def".

ListHTML = "";     # value is ""
ListHTML = "abc";  # value is "abc"
ListHTML += "def"; # value is "abcdef"

Instead of just counting the correct and wrong answers, we want to save the questions associated with the right and wrong answers. Each question is a string. These string are stored in two arrays, named 'correct' and 'wrong'. The [] at the end of the variable declaration tell us that this is an array.

question = 'How many states are in the United States?'
var correct = [];   # creates an empty array
correct.push(question)
    # now there is one element in the array:
    # [ 'How many states are in the United States?' ]

correct.push(question)
    # now there are two elements in the array:
    # [ 'How many states are in the United States?', 'How many states are in the United States?' ]

I am not sure what you mean by "undefined on top".

Darien Kim
Darien Kim
3,126 Points
Darien Kim
Darien Kim
3,126 Points

Thank you for your explanation, I relaunched Workspace and the unidentified doesn't appear now.