Help with getting input text to use in function

JavaScript
1

I’m having a hard time understanding why my alert is popping up without pressing the button and also why I am not able to get the text from the input box to use in my functions.

<!DOCTYPE html>

<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>Palindrome Checker</title>
    <link rel="stylesheet" type="text/css" href="./styles.css">
    </head>
    <body>
      <header>
        <h1 id="title">Christian's palindrome checker</h1>
        <h2>Type a word or sentence below and click the button to check if it is a palindrome.</h2>
      </header> 
      <form>
  <input type="text" id="text-input">
  <br />
  <button id="check-btn" >Check!</button>
  <p id="result"></p>
  </form>
<script src="./script.js"></script>
      </body>

  </html>

html {
  font-size: 62.5%;
  font-family: sans-serif;
  text-align: center;
}

h1 {
  font-size: 4rem;
}

h2 {
  font-size: 2rem;
}

const userInput = document.getElementById("text-input").value;

const checkButton = document.getElementById("check-btn");

const resultText = document.getElementById("result")


function cleanString(string) {
const regex = /[^a-zA-Z0-9]/gi;
  const lowerCaseString = string.toLowerCase()
  return lowerCaseString.replace(regex, "");
}
 
function checkForPalindrome(userInput) {
  if (userInput === "") {
    return alert("Please input a value")
  } else {
  const cleanText = cleanString(userInput);
  const cleanTextArray = cleanText.split("");
  const reverseTextArray = cleanTextArray.reverse();
  const reverseText = reverseTextArray.join("");
  if (reverseText === cleanText) {
    return resultText.innerText = `${userInput} is a palindrome`;
  } else {
    return resultText.innerText = `${userInput} is not a palindrome`;
  }
  }
}
checkButton.onclick = checkForPalindrome(userInput);
2

Onclick is expecting a function reference but you are not referencing the function here. Rather you are calling the function on window load here.

3

Also, this will get the value when the page loads not when the user clicks the button.