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<!DOCTYPE html> <html> <body> <h1>JavaScript Global Methods</h1> <h2>The isNaN() Method</h2> <p>isNaN() returns true if a value is NaN:</p> <p id="demo"></p> <script> let result = "Is 'NaN' NaN? " + isNaN('NaN') + "<br>" + "Is NaN NaN? " + isNaN(NaN) + "<br>" + "Is undefined NaN? " + isNaN(undefined) + "<br>" + "Is null NaN? " + isNaN(null); document.getElementById("demo").innerHTML = result; </script> </body> </html>