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