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Looping through array and back to beginning when reaching end

I have a simple array
var answerAttribute = ['A','B','C','D'];
I have 16 list items, what I'm trying to accomplish is loop through the length of the list and regardless of if the list 2 items or 300. I'd lke to have a data attribute associated with it of A,B, C or D.
Here's what I'm working with:
var questionOption = '';
for(var i = 0; i < quizContent.length; i++) {
questionOption = answerAttribute[i % answerAttribute.length];
console.log(questionOption);
}
When logging this to the console, it logs A, AB, ABC, ABCD, ABCDundefined, and keeps repeating undefined until it's reached the loops conclusion. My question is what am I doing incorrectly so that it only logs one letter per loop.

questionOption += answerAttribute[i]
This statement is short-form for questionOption = questionOption + answerAttribute[i]. It will append the next element to questionOption in every iteration of the loop.
It looks like what you want is probably questionOption = answerAttribute[i]. This will replace the value in questionOption with the new element instead of appending it.

You could simply log only the current value, like this:
var questionOption = '';
for (var i = 0; i < quizContent.length; i++) {
//what is questionOption used for?
questionOption += answerAttribute[i];
console.log(answerAttribute[i]);
}
or if you want questionOption to refer to the current value
questionOption = answerAttribute[i];
console.log(questionOption );

You're looping the quizContent indexes and applying them to the answerAttribute array. I believe what you want is a nested loop...
var quizContent = Array(10); // assume you have 10 quiz questions...
var answerAttribute = ['A','B','C','D'];
for (var i = 0; i < quizContent.length; i++) {
// generate a string for each quiz option
var questionOption = '';
for (var n = 0; n < answerAttribute.length; n++) {
questionOption += answerAttribute[n];
}
quizContent[i] = questionOption;
console.log(questionOption);
}
console.log(quizContent);

Somehow I doubt that the question is actually about the logging, and is actually about the resulting string.
Either way, I'd do this without loops.
var answerAttribute = ['A','B','C','D'];
var quizContent = [1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1];
var questionOption = answerAttribute
.join("")
.repeat(Math.ceil(quizContent.length / answerAttribute.length))
.slice(0, quizContent.length);
console.log(questionOption);
It just joins the answerAttribute into a string of characters, and repeats that string the number of times that the length of answerAttribute can be divided into quizContent.length (rounded up).
Then the final string is trimmed down to the size of the quizContent to remove any extra content from the rounding up.
Note that this approach assumes a single character per attribute. If not a single, but they're all the same length, it can be adjusted to still work.

JS: Reversing a string using nested loop does not work

I have written a function called reverseStr that takes in a string as a parameter and returns the string but with the characters in reverse.
For example: reverseStr('bootcamp'); => 'pmactoob'
Following is my program:
function reverseStr(str)
{
var splitStr = str.split("");
console.log(splitStr);
var reverseString = [];
for(var i = 0; i <= splitStr.length -1 ; i++)
{
for(var j = splitStr.length - 1; j >= 0; j--)
{
reverseString[i] = splitStr[j]
}
}
return reverseString.toString().replace(/[&\/\\#,+()$~%.'":*?<>{}]/g, '');
}
If I run the function reverseStr("bootcamp") it returns bbbbbbbb.
Does anyone see a problem with the code?
Note: I DONOT WANT TO USE REVERSE() BUILT-IN FUNCTION
However, I found success with the following code but still need an answer to my initial question
function reverseStr(str)
{
var splitStr = str.split("");
reverseStr = "";
for(var i = splitStr.length - 1; i >= 0 ; i = i - 1)
{
reverseStr += splitStr[i];
}
return reverseStr;
}

You don't need to double-iterate through the characters, i.e., do not need to nest for loops. Iterate once and grab the chars in reverse order, like this:
function reverseStr(str)
{
var splitStr = str.split("");
console.log(splitStr);
var reverseString = [];
for(var i = 0, j=splitStr.length-1; i <= splitStr.length -1 ; i++, j--)
{
reverseString[i] = splitStr[j]
}
return reverseString.toString().replace(/[&\/\\#,+()$~%.'":*?<>{}]/g, '');
}
You can see that here the loop goes on for as long as i <= splitStr.length -1,ie, length of the string. This is sufficient to get the mirroring character (i versus Array.length-i).
Here is a working snippet to demo:
var reverseStr = function(str) {
let result = String();
for(let i = str.length-1; i >= 0; i--) {
result += str.charAt(i);
}
return result.replace(/[&\/\\#,+()$~%.'":*?<>{}]/g, '');
}
$('button').click(function() {
$('.result').text(reverseStr($('#str').val()));
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="text" id="str">
<button>Reverse it</button>
<div class="result"></div>
Perhaps a more elegant way to achieve the same (apart from Array.prototype.reverse()) would be to use String.prototype.chatAt(). This would avoid two conversions to and from an array, and also save you one variable. Granted, the code is much shorter and more obvious in what it is doing.
var reverseStr = function(str) {
let result = String(); // An empty string to store the result
for(let i = str.length-1; i >= 0; i--) { // Iterate backwards thru the chars and add to the result string
result += str.charAt(i);
}
return result.replace(/[&\/\\#,+()$~%.'":*?<>{}]/g, ''); // Original return method of the author
}
$('button').click(function() {
$('.result').text(reverseStr($('#str').val()));
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="text" id="str">
<button>Reverse it</button>
<div class="result"></div>

The problem is that your nested for loop runs its whole course before it returns to the outer for loop. So, it just repeats one character the amount of times equal to the length. Instead of having another for loop, just add a simple counter for j like j++ inside your outer for loop and use that value with the i value.

To the original poster, consider this:
If you know the length of the original string, you therefore know the offset of that last position within the original string.
Iterate through the original string in reverse order, appending the current position's value to a new string. The new string would be the reverse of the original.

Aydin's example is essentially correct. Here's my very similar version, with comments:
function reverseString(inputString) {
// create a new empty string
var newString = "";
// iterate through the characters of the string in reverse order,
// appending to the new string
for (var i = inputString.length - 1; i >= 0; i--) {
newString += inputString[i];
}
return newString;
}
console.log(reverseString('bootcamp'));

Splice NOT removing certain characters

I'm working on some codewars problems and I came to this 'remove noise thing', I guess the point is to escape backslash \ and use replace method, which was easy. But I didn't want to use replace, instead I found myself in trouble trying to remove items with splice method.
Funny thing is, when I debug in Chrome dev tools, step by step I see items get removed, but console.log spits out certain characters($/·|ªl) problematic to remove, and at the end gets returned and join with those characters. Why is that?
function removeNoise(str) {
var base = "%$&/#·#|º\ª";
var arr = str.split('');
for(var i = 0; i < arr.length; i++) {
var item = arr[i];
var condition = base.indexOf(item);
if(condition + 1) {
//works like a charm
//arr[i] = '';
arr.splice(i,1);
//this thing wont work
//when debugging it removes the items from the array
//console log print no removing
}
}
return arr.join('');
}
removeNoise('he%$&/#·#|º\ª\llo'); //=> $/·|ªllo

You're using splice to remove entries from your array, but you're then incrementing i for the next loop. If you remove the entry at index 5 from a 10-entry array, what was the entry at index 6 is now at index 5 (of what's now a 9-entry array), so you don't want to increment your index.
The solution is to use a while loop and only update i if you don't splice:
function removeNoise(str) {
var base = "%$&/#·#|º\ª";
var arr = str.split('');
var i = 0;
while (i < arr.length) {
var item = arr[i];
var condition = base.indexOf(item);
if (condition + 1) {
// Remove this entry, reuse same value for 'i'
arr.splice(i,1);
} else {
// Don't remove this entry, move to next
++i;
}
}
return arr.join('');
}
var result = removeNoise('he%$&/#·#|º\ª\llo');
var pre = document.createElement('pre');
pre.appendChild(
document.createTextNode(result)
);
document.body.appendChild(pre);

You're removing characters from your array. This will throw your indexer variable i out of sync with the characters you want to test. Easy way to fix is to start at the end of the array working your way to the beginning.
Change your for loop to this.
for(var i = arr.length -; i <= 0; i--) {
function removeNoise(str) {
var base = "%$&/#·#|º\ª";
var arr = str.split('');
for(var i = arr.length - 1; i <= 0 ; i--) {
var item = arr[i];
if(base.indexOf(item) >= 0) {
//remove the offending character
arr.splice(i,1);
}
}
return arr.join('');
}
removeNoise('he%$&/#·#|º\ª\llo'); //=> $/·|ªllo

Find the nth character from an array of words in JavaScript

I'd like to create a function (nthChar) that takes 1 parameter - an array of n words.
The function should concatenate the nth letter from each word to construct a new word which should be returned as a string.
The nth letter should be the 1st from the first word in the array, the second from the second word in the array, the third from the third and so on. So:
nthChar(['I','am','Tom']) should return 'Imm'
Here's my attempt:
function nthChar(words){
for (var i=0; i<words.length; i++) {
return words[i].charAt(words.indexOf(words[i]))
}
}
Which only seems to grab the first letter of the first word. How would I proceed to the other words of the array before concatenation?

With minimal changes to your code, you can do this
function nthChar(arr) {
var str = '';
for (var i=0; i<words.length; i++) {
str = str + words[i][i];
}
return str;
}
str - used to build up the result string
words[i] selects the i'th word ... the second [i] in that statement selects the i'th letter in that word
for example: "Hello World"[6] is W
Bonus: works in IE8 and earlier ...
and, just for the hell of it, void's answer in ES6
var nthChar = arr => arr.map((i, v) => i[v]).join('');

This can be as simple as
function nthChar(words){
var s = "";
for(var i=0;i<words.length;i++){
s+= words[i].charAt(i);
}
return s;
}
Live example: http://jsfiddle.net/11yc79jn/
This is closest to your original solution, and just uses the loop control variable i which is incrementing already as you loop through the words array. Of course, also return after the entire loop has run as well.

function nthChar(arr){
return arr.map(function(i, v){
return i[v];
}).join("");
}
console.log(nthChar(['I','am','Tom']));
So it is returning an array of the characters you want and then it is joining it. Makes sense?
The issue with your code was that you were not concatenating anything to the output. You can access the characters of a string as if it is an array.
Live Fiddle
Your code can be:
function nthChar(words){
var str = "";
for (var i=0; i<words.length; i++) {
str += words[i].charAt(i);
}
return str;
}
Fiddle

Try something like this
function nthChar(words){
var result = "";
for (var i = 0, ln = words.length; i<ln; i++)
result += words[i].charAt(i);
return result;
}

Get concatenate string of multiple value variable in Javascript

I've a list of div
<div data-attr="sel" data-num="1"></div>
<div data-attr="notSel" data-num="2"></div>
<div data-attr="sel" data-num="3"></div>
I'm tryng to get a string only div with the data-attr="sel" set.
function SI_MoveTasks() {
var getSelected = document.querySelector('[data-attr~="sel"]');
var selectedNums = getSelected.dataset.num;
alert(selectedNums);
}
Now i get (1), how can i get the concatenate string (1,3)?
Thanks for support.

DEMO -> http://jsfiddle.net/0d54ethw/
Use querySelectorAll instead of querySelector since the latter only selects the first element as opposed to all of them.
Then use for loop as shown below
var getSelected = document.querySelectorAll('[data-attr~="sel"]');
var selectedNums = [];
for (var i = 0; i < getSelected.length; i++) {
selectedNums.push(getSelected[i].dataset.num);
}
alert(selectedNums.join(','));

You would need to use document.querySelectorAll to get all matching elements. document.querySelector returns only the first matching element, or null if there is none.
function SI_MoveTasks() {
var getSelected = document.querySelectorAll('[data-attr~="sel"]');
console.log(getSelected);
var selectedNums = '(';
for(var i=0; i< getSelected.length; i++) {
if (selectedNums !== '(') {
selectedNums += ',';
}
selectedNums += getSelected[i].dataset.num;
}
selectedNums += ')';
alert(selectedNums);
}
SI_MoveTasks();
Thats a working code, jsFiddle is: https://jsfiddle.net/3kjye452/