running a mini address book to see how changing extensibility for objects works in js

extensibility.js

"use strict()";

// make a phoneBook object
var phoneBook  = {};

// add some people objects
phoneBook.bob= {name:"Bob",age:35};
phoneBook.greg= {name:"Greg",age:27};
phoneBook.nancy= {name:"Nancy", age:65};

//iterate over each item in the phoneBook
// `item` will be returned as a String so use [] method to acces properties
var list = function (){
	for(var entry in phoneBook) {
	  var person = phoneBook[entry] //a person in the phoneBook
		console.log("Name: " + person.name + " Age: "+ person.age );
	//	console.log(person);
	}
};
list()
Object.preventExtensions(phoneBook);

phoneBook.julie = {name:"Julie", age:45}
console.log("*********************")
console.log(Object.isExtensible(phoneBook));
list()
// MDN:   https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...in