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<!DOCTYPE html> <html> <body> <p>Click the button, and display "green" if a boolean value is <em>true</em>, otherwise display "red".</p> <button onclick="myFunction()">Try it</button> <p id="demo"></p> <script> Boolean.prototype.myColor = function() { if (this.valueOf() == true) { return "green"; } else { return "red"; } }; function myFunction() { var a = true; document.getElementById("demo").innerHTML = a.myColor(); } </script> </body> </html>