Wsrtjtyk

let getId = x => document.getElementById(x);

let banned = ['word1','word2','word3'];

let start = 0;



getId('censor').addEventListener('click', function(){

let stars = '';

for(let i=0;i < banned[0].length; i++) {

    stars+= '*';

}

let str = getId('text').value;

str = str.split(' ');

let found = str.indexOf(banned[0],start);

str.splice(found,1, stars);

str = str.join(' ');

getId('text').value = str;

})

<div class="container">

    <form action="">

        <input type="text" id="banInput">

        <input type="button" value="Add word" id="add">

    </form>

    <textarea name="" id="text"></textarea>

    <input type="button" value="censor" id="censor">

</div>

let getId = x => document.getElementById(x);

let banned = ['word1', 'word2', 'word3'];



getId('add').addEventListener('click', function() {

  banned.push(getId('banInput').value)

  getId('banInput').value = ''

  console.log(banned)

})



getId('censor').addEventListener('click', function() {



  let str = getId('text').value;

  let arr = str.split(/b/) // array of words

  let censored = arr.map(word => banned.includes(word) ? //if word is in banned

    '*'.repeat(word.length) // replace with *

    :

    word) // leave as is



  getId('text').value = censored.join(''); // back to string

})

<div class="container">

  <form action="">

    <input type="text" id="banInput">

    <input type="button" value="Add word" id="add">

  </form>

  <textarea name="" id="text"></textarea>

  <input type="button" value="censor" id="censor">

</div>

//Censor function

var censored = ;

function censor(input) {

    return input.replace(/w+/igm, function (word) {

        if (censored.some(function (cWord) { return cWord.toLowerCase() === word.toLowerCase(); })) {

            return word.replace(/./igm, '*');

        }

        return word;

    });

}

// HTML NODES

var inputField = document.body.appendChild(document.createElement("textarea"));

var outputField = document.body.appendChild(document.createElement("textarea"));

outputField.readOnly = true;

document.body.appendChild(document.createElement("br"));

var listInput = document.body.appendChild(document.createElement("input"));

listInput.title = listInput.placeholder = "insert censored words, seperate by " "";

listInput.value = '';

//Update functions

function updateOutput() {

    outputField.value = censor(inputField.value);

}

function updateCensorList() {

    censored = listInput.value.split(" ");

    if (censored == null) {

        censored = [''];

    }

    else {

        censored = censored.map(function (a) { return a.trim(); });

    }

    updateOutput();

}

//Bind events

listInput.addEventListener("change", updateCensorList);

listInput.addEventListener("keyup", updateCensorList);

inputField.addEventListener("change", updateOutput);

inputField.addEventListener("keyup", updateOutput);