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<!DOCTYPE html> <html> <body> <p>Input your age and click the button:</p> <input id="age" value="18" /> <button onclick="myFunction()">Try it</button> <p id="demo"></p> <script> function myFunction() { var age, voteable; age = Number(document.getElementById("age").value); if (isNaN(age)) { voteable = "Error in input"; } else { voteable = (age < 18) ? "Too young" : "Old enough"; } document.getElementById("demo").innerHTML = voteable; } </script> </body> </html>