Call function when text changed

<form >
  <textarea id="MyTextArea" ></textarea>
</form>

<script>
document.getElementById('MyTextArea').addEventListener('input', function () {
  console.log('MyTextArea changed:', this.value);
    
  //You can alos use this to gets its value:
  //console.log(document.getElementById('MyTextArea').value);
});
</script>