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HTML 

              
                <div id="top-half">
  <form id="top-half-content">
    <label for="palindrome-check">Is it a palindrome?</label>
    <input id="palindrome-check" type="text" name="palindrome-check" placeholder="Ex: Racecar">
  </form>
</div>

<div id="bottom-half">
  <p id="output">Nothing's been entered...</p>
</div>
!

CSS 

              
                /*Variables*/
$primary-default: #152B42;
$primary-light: #1159A6;
$primary-dark: #152B42;

$primary-default-text: white;
$primary-light-text: black;
$primary-dark-text: white;

$font-family: 'Kufam', cursive;

/*Styles*/
body {
  font-family: $font-family;
  margin: 0;
  padding: 0;
}

#top-half {
  //Layout
  position: relative;
  width: 100vw;
  height: 50vh;
  min-height: 200px;
  
  //Text
  line-height: 50vh;
  
  //Design
  color: $primary-default-text;
  background-color: $primary-default;
  
  form {
    //Layout
    position: relative;
    display: inline-block;
    width: 100vw;
    height: 50vh;
    
    //Text
    text-align: center;
    line-height: 2rem;
    
    label {
      //Layout
      position: relative;
      width: 100vw;
      
      //Text
      font-size: 30px;
      font-weight: bold;
    }
    
    input {
      //Layout
      position: relative;
      width: 80%;
      height: 8vh;
      min-height: 40px;
      padding: 10px;
      
      //Text
      text-align: center;
      
      //Design
      border-radius: 20px;
      border: 0;
      outline: none;
      box-shadow: 0 0 5px black;
    }
  }
}

#bottom-half {
  //Layout
  position: relative;
  width: 100vw;
  height: 50vh;
  min-height: 200px;
  border: 1px solid;
  
  //Text
  font-size: 20px;
  line-height: 50vh;
  text-align: center;
  
  //Design
  color: $primary-dark;
  
  p {
    //Layout
    position: relative;
    display: inline-block;
    
    //Text
    line-height: 1.5rem;
  }
}
!

JS 

              
                //Grab DOM objects
const palindromeCheck   = document.querySelector('#palindrome-check');  //The user input box
const output            = document.querySelector('#output');  //The output <p> tag

//Functions
let palindrome = (str) => {
  let alphaCheck = /[a-z0-9]/i;
  let alphaArr = str
    .toLowerCase()
    .split('')
    .filter(char => alphaCheck.test(char));
  if (alphaArr.length === 0) { return false; }
  for (let i = 0; i <= Math.floor(alphaArr.length/2); i++) {
    if (alphaArr[i] !== alphaArr[alphaArr.length - 1 - i]) {
      return false;
    }
  }
  return true;
};

let generateListeners = () => {
  palindromeCheck.addEventListener('input', generateOutput);
};

let generateOutput = (e) => {
  //Grab input
  let input = e.target.value;
  let inputArr = input.split(''); 
  
  //Ensure input is /[a-z0-9]/ only
  let inputTest = /[a-z0-9]/i;
  inputArr = inputArr.filter(char => inputTest.test(char));
  
  //Display clean text and continue
  e.target.value = inputArr.join('');
  input = inputArr.join('');
  
  if (input === '') { //Check to see if the input is empty
    output.textContent = "Nothing's been entered...";
  } else { //If it isn't, process input
    let checkValue = palindrome(input);

    if (checkValue) {
      console.clear(); console.log(output.target);
      output.textContent = "Yep, that's definitely a palindrome!";
    } else {
      output.textContent = "Nope, not a palindrome...";
    }
  }
};

//Generate listeners
generateListeners();
!
999px

Console