From 49b228eac3c1524c4fb1fd78c3a3171d673adcca Mon Sep 17 00:00:00 2001
From: Md-Asraful-Islam-Subbir
 <93644909+Md-Asraful-Islam-Subbir@users.noreply.github.com>
Date: Sat, 20 Dec 2025 19:05:29 +0600
Subject: [PATCH] explain updated

---
 day-12/index.js | 69 +++++++++++++++++++++++++------------------------
 1 file changed, 35 insertions(+), 34 deletions(-)

diff --git a/day-12/index.js b/day-12/index.js
index b719d8d..6f629a1 100644
--- a/day-12/index.js
+++ b/day-12/index.js
@@ -3,7 +3,7 @@ console.log("Day 12 - JavaScript Objects");
 let user = {
     name: "tapas",
     age: 40,
-    "is adimin": true
+    "is adimin": true  // multi word property
 };
 
 console.log(user.name); // "tapas"
@@ -13,7 +13,7 @@ user.isSeniorCitizen = false;
 user["movie lover"] = true;
 
 console.log(user);
-
+// Accessing multi word property
 console.log(user["is adimin"]);
 
 user.age = 34;
@@ -22,7 +22,7 @@ user["movie lover"] = false;
 // delete user["movie lover"];
 // delete user.age;
 console.log(user)
-
+// Dynamic Property Access
 const someKey = "age";
 
 console.log(user[someKey]); // 34
@@ -40,21 +40,22 @@ function Car(name, model) {
     this.name = name;
     this.model = model
 }
-
+//here Car is uppercase because it is a constructor function,
+// so by convention we use uppercase for constructor functions
 const bmwCar = new Car("BMW", "X1");
 const audiCar = new Car("Audi", "A8");
 console.log(bmwCar)
 console.log(audiCar)
 
 console.log(bmwCar instanceof Car);
-
+// Object Creation using Object Constructor
 const person = new Object()
 person.name = "Alpha";
 person.age = 76;
 console.log(person);
 
 
-// factory
+// factory function means a function that returns an object
 function createUser(name, age) {
     return {
        name,
@@ -66,13 +67,14 @@ function createUser(name, age) {
 }
 
 const user1 = createUser("tapas", 39)
-console.log(user1)
+console.log(user1) // {name: "tapas", age: 39, greet: ƒ}
 user1.name;
 user1.age;
 user1.greet();
 const user2 = createUser("bob", 32)
 console.log(user2)
 
+// Nested Objects
 let profile = {
     name: "tapas",
     company: "CreoWis",
@@ -89,23 +91,23 @@ let profile = {
         }
     }
 }
-// for ... in
+// for ... in use to iterate over object properties
 
 for (let key in profile) {
     console.log(key)
     console.log(profile[key]);
 }
+//here Object.keys() method returns an array of a given object's own enumerable property names
+console.log(Object.keys(profile)); // ["name", "company", "message", "address"]
 
-console.log(Object.keys(profile));
-
-console.log(profile.salary); // undefined
+console.log(profile.salary); // undefined because salary property doesn't exist
 
-console.log("salary" in profile);
+console.log("salary" in profile); // false
 
 if (!profile.salary) {
     console.log("The salary property doesn't exist");
 }
-
+// Accessing Nested Object Properties
 console.log(profile.address.country); // India
 profile.address.greeting();
 console.log(profile.name);// "tapas"
@@ -127,18 +129,18 @@ fruit = oneMoreFruit;
 console.log(fruit == oneMoreFruit); // true
 console.log(fruit === oneMoreFruit); // true
 
-// Static Methods
+// Static Methods used with Objects
 
 const target = {p:1, a:2};
 const source = {a:3, b:5};
-
+//object.assign(target, source) method copies all enumerable own properties from one or more source objects to a target object. It returns the modified target object.
 const retrunedObj = Object.assign(target, source);
-console.log(retrunedObj);
+console.log(retrunedObj);// {p: 1, a: 3, b: 5} a:2 is overwritten by a:3 because b property doesn't exist in target object
 
 const obj = {name: "tapaScript"};
 const obj2 = Object.assign({}, obj);
-console.log(obj2)
-console.log(obj === obj2)
+console.log(obj2)  // {name: "tapaScript"}
+console.log(obj === obj2) // false
 
 const obj3 = {
     a: 1,
@@ -148,7 +150,7 @@ const obj4 = Object.assign({}, obj3);
 console.log(obj4); // {a: 1, b: {c: 2}}
 // obj4.b.c = 3;
 
-// obj4.a = 100;
+// obj4.a = 100; 
 
 // console.log(obj4.a); // 100
 // console.log(obj3.a); // 1
@@ -173,44 +175,43 @@ const myObj = {
     a: "tapas",
     b: 32,
 };
-
-const myArr = Object.entries(myObj);
-console.log(myArr)
+// Object.entries() method returns an array of a given object's own enumerable string-keyed property [key, value] pairs.
+const myArr = Object.entries(myObj); // [['a', 'tapas'], ['b', 32]]
+console.log(myArr) //object to array conversion
 
 const entries = new Map([
     ["foo", "bar"],
     ["baz", 42],
 ]);
-const objEntries = Object.fromEntries(entries)
-console.log(objEntries);
-
+const objEntries = Object.fromEntries(entries) // converts a list of key-value pairs into an object
+console.log(objEntries); // array to object conversion {foo: "bar", baz: 42}
 
 const emp = {
     sal: 100
 }
-
+// Freezing an Object which makes it immutable but shallowly 
 Object.freeze(emp);
 
-emp.sal = 200;
-emp.name = "Alex";
+emp.sal = 200; // won't work because object is frozen
+emp.name = "Alex"; // won't work because object is frozen
 delete emp.sal;
 
-console.log(emp)
+console.log(emp) // {sal: 100}
 
-console.log(Object.isFrozen(emp));
+console.log(Object.isFrozen(emp)); // true
 
 
 const dept = {
     name: "finance"
 }
 
-Object.seal(dept);
+Object.seal(dept); // makes the object sealed but shallowly 
 
-dept.address = "Bangalore"
+dept.address = "Bangalore" // won't work because object is sealed
 delete dept.name;
 
-dept.name = "HR"
-console.log(dept)
+dept.name = "HR" // works because we can modify existing properties in sealed object
+console.log(dept) // {name: "HR"}
 
 console.log(Object.hasOwn(dept, "address"))