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<!DOCTYPE html> <html> <body> <h1>JavaScript Objects</h1> <h2>The Object.preventExtensions() Method</h2> <p id="demo"></p> <script> "use strict" // Create Object const person = {firstName:"John", lastName:"Doe"}; // Prevent Extensions Object.preventExtensions(person) // Test Error let text = ""; try { person.nationality = "English"; } catch (err) { text = err; } document.getElementById("demo").innerHTML = text; </script> </body> </html>
