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<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <title>JavaScript Dynamically Add a Key Value Pair to an Object Using Variables</title> <script> // Sample object var myCar = { make: "Ferrari", model: "Portofino", year: 2018 }; // Sample variables var myKey = "fuel"; var myValue = "Petrol"; // Dynamically adding a key/value pair myCar[myKey] = myValue; document.write(JSON.stringify(myCar)); </script> </head> <body style="font-family: monospace;"> <!-- Object will be printed here --> </body> </html>