Also consider .replace(/\*\*\*/g, '0') if you want to replace multiple occurrences of ***. (The below code only replaces the first occurrence in each string.)

stuff= ["uyuuyu", "76gyuhj***", "uiyghj", "56tyg", "juijjujh***"];

for(var i = 0; i < stuff.length; i++)
{
    stuff[i] = stuff[i].replace('***', '0');
}

console.log(stuff);

Note that there's no need to check indexOf. If the substring isn't present, the replace just doesn't change anything, so you can just apply the replace to every string.

Strings are immutable, so you just have to re-assign their value:

vertices[x] = vertices[x].replace('v ', '');

Both your methods (setCharAt and replaceAt) are returning the result, which means you have to set it:

function delCookie() {
   cookies.splice(0,1);
   cookies[0] = cookies[0].replaceAt(8, "Z"); 
   //or
   // cookies[0] = setCharAt(cookies[0], 8, "Z");
}

I am creating an object letters which will get all the letters as the key and the value is an array with all the index of the letter in the word.

eg: The word hey will have the object like

{
    "h":[0],
    "e":[1],
    "y":[2]
}

I am using Array#map() to create an array of stars.

To know where to put the letter instead of a star I am using Array#find() to find the key with the letter typed. If the result is undefined - it means that the letter you tried is not in the word. If it is defined, I replace the star at the index of the letter with the correct letter

$(document).ready(function() {

  $('#div_letter').hide();
  var word_input = $('#word');
  var word_array = [];
  var letters = {};

  word_input.keypress(function(e) {
    if (e.keyCode == 13) {
      word_array = Array.from(word_input.val());
      letters = word_array.reduce((obj,letter, i)=>{
        obj[letter] = obj[letter] || [];
        obj[letter].push(i);
        return obj;
      }, {});
      var stars = word_array.map(l=>"*");
      
      $('#div_word').hide();
      $('#div_letter').show();
      $('#display').text(stars.join(""));

      $('#letter').keypress(function(e) { //if any key is pressed
        var _letter = $(this);
        var char = String.fromCharCode(e.which).toLowerCase(); //get which key
        
        let keyLetter = Object.keys(letters).find(l=>l.toLowerCase()===char);
        if(keyLetter){
          letters[keyLetter].forEach(i=>stars[i] = char);
          $('#display').text(stars.join(""));
        }
        _letter.val("");
      });
    }
  });
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.js"></script>
<div id="div_word">
  <label>Enter your Word</label>
  <input id="word" type="text"><br>
</div>

<div id="div_letter">
  <label>Type a letter</label>
  <input id="letter" type="text" /><br>
</div>

<label>Display Array:</label>
<div id="display">

</div>

One option is to stringify the object, replace, then parse it:

const testArray = [
  { ASIN: 'ABC123', Rank: '£50', Sales: '£80' },
  { ASIN: 'ZYX123&', Rank: '£70', Sales: '£20' },
];

const newTestArray = JSON.parse(
  JSON.stringify(testArray).replaceAll('£', '')
);
console.log(newTestArray);

Could also transform the object by mapping with Object.fromEntries:

const testArray = [
  { ASIN: 'ABC123', Rank: '£50', Sales: '£80' },
  { ASIN: 'ZYX123&', Rank: '£70', Sales: '£20' },
];
const newTestArray = testArray.map(
  obj => Object.fromEntries(
    Object.entries(obj)
      .map(([key, val]) => [key, val.replaceAll('£', '')])
  )
);
console.log(newTestArray);

You could globally match ___ using the /g flag and get the index of the replacement from blankData be seeding a start value of 0 and increment it in every iteration.

const text = 'hello ___ where ___ test ___';
const blankData = ['there', 'you', 'it'];

result = text.replace(/___/g, (i => _ => blankData[i++])(0));

console.log(result);

Note that if you don't want to have multiple matches for _________ but also don't want to match a single _ you can use _{3,} as the pattern to match 3 or more times an underscore.

const text = 'h_ello ______ where ___ test ___';
const blankData = ['there', 'you', 'it'];

result = text.replace(/_{3,}/g, (i => _ => blankData[i++])(0));

console.log(result);

This should work.

let names = ["Fern", "Alexa", "Constance", "Daniella", "Connie", "Flora", "Hannah", "Maddie"];

let modified = names.map(e => e.replace(e[0], 'B'))

console.log(modified);

you can use escape the RegExp special characters in the strings such as described here https://stackoverflow.com/a/6969486/519995:

and then you can use the regexp global replace

function escapeRegExp(str) {
   return str.replace(/[\-\[\]\/\{\}\(\)\*\+\?\.\\\^\$\|]/g, "\\$&");
}

for (startChar in charMap) {
   endChar=charMap[startChar];
   result = string.replace(RegExp(escapeRegExp(startChar), 'g'), endChar);
}

You can try this code:

a = "{12,a},b,c,{c,d}";
m = a.match(/{[^}]*}|[^,]+/g);
arr=[];

for (i=0; i<m.length; i++) {
    if (m[i].indexOf('{') >= 0)
        arr.push(m[i].replace(/[{}]/g, "").split(/,/));
    else
    arr.push(m[i]);
}
console.log(arr);

OUTPUT:

[[12,a],b,c,[c,d]]

Use String.replace() with a function that generates the replacement string. In the function get the current replacement from newWords using a counter:

function replaceAsterisk(sentence, newWords) {
  let counter = 0;
  
  return sentence.replace(/\*/g, () => newWords[counter++] || '');
}

console.log(replaceAsterisk("My name is * and I am a *.", ["Sabrina", "Black Cat", "extra", "words"]));

You need to use a regular expression with the global option set to replace all of the instances. But, you can also simplify this code a bit and get rid of the loop. Instead of Arrays, use an object:

var alphabet = {
    'a': 'ⴰ',
    'b': 'ⴱ',
    'g': 'ⴳ',
    'gw': 'ⴳⵯ',
    'd': 'ⴷ',
    'ḍ': 'ⴹ',
    ...
    'z': 'ⵣ',
    'ẓ': 'ⵥ'
};

Then use a regular expression with a replacement function:

var word = $("input[name=word]").val();
var tifinaghized = word.replace(/[abgdḍefkhḥɛxqijlmnurṛɣsṣctṭwYzẓ]|gw|kw/g, function(s) {
    return alphabet[s];
});

Working demo: http://jsfiddle.net/gilly3/MdF6R/

Yes.

for(var i=0; i < arr.length; i++) {
 arr[i] = arr[i].replace(/,/g, '');
}

Usually, the result of the replace function is returned as a new String object in most of the programming languages. You should change your code to this:

if (name.charAt(i) === charList[j])
    name = name.replace(name.charAt(i), replaceList[j]);

Also, since the replace function will replace all the occurrences of that character, you could change your algorithm a little bit.