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<!DOCTYPE html>
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.7.1/jquery.min.js"></script>
<script>
$(document).ready(function(){
  $("input").change(function(){
    alert("The text has been changed.");
  });
});
</script>
</head>
<body>
<input type="text">
<p>Write something in the input field, and then press enter or click outside the field.</p>
</body>
</html>