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Objects in JavaScript

📜 Original Code​

const descriptor = Object.getOwnPropertyDescriptor(Math, 'PI');

// console.log(descriptor);

// console.log(Math.PI);
// Math.PI = 5
// console.log(Math.PI);

const chai = {
  name: 'ginger chai',
  price: 250,
  isAvailable: true,

  orderChai: function () {
    console.log('chai nhi bni');
  }
};

console.log(Object.getOwnPropertyDescriptor(chai, 'name'));

Object.defineProperty(chai, 'name', {
  //writable: false,
  enumerable: true
});

console.log(Object.getOwnPropertyDescriptor(chai, 'name'));

for (let [key, value] of Object.entries(chai)) {
  if (typeof value !== 'function') {
    console.log(`${key} : ${value}`);
  }
}

🔹 What’s Happening in the Code?​

1️⃣ Object.getOwnPropertyDescriptor() - Getting Property Attributes​

const descriptor = Object.getOwnPropertyDescriptor(Math, 'PI');
console.log(descriptor);

Why does this work?

  • Math.PI is a built-in property of JavaScript.
  • Object.getOwnPropertyDescriptor() retrieves metadata about the property.
  • The output will be: 
    {
      value: 3.141592653589793,
      writable: false,
      enumerable: false,
      configurable: false
    }
    Trivia:
  • Since writable: false, you cannot change Math.PI.
  • Since enumerable: false, it won’t appear in for...in loops.
  • Since configurable: false, you cannot delete or redefine it.

2️⃣ Trying to Modify Math.PI​

console.log(Math.PI);
Math.PI = 5;
console.log(Math.PI);
  • Since writable: false, reassigning Math.PI will have no effect.
  • console.log(Math.PI); still prints 3.141592653589793.

3️⃣ Understanding Property Descriptors in Custom Objects​

console.log(Object.getOwnPropertyDescriptor(chai, 'name'));

Output:

{
  value: 'ginger chai',
  writable: true,
  enumerable: true,
  configurable: true
}
  • Default object properties in JavaScript are:
    • writable: true → Can be changed
    • enumerable: true → Appears in loops
    • configurable: true → Can be deleted or modified

4️⃣ Modifying Property Descriptors with Object.defineProperty​

Object.defineProperty(chai, 'name', {
  // writable: false,  // Uncommenting this will prevent changes
  enumerable: true
});
  • We updated name's descriptor.
  • If writable: false is added, chai.name = 'masala chai' won’t work.
  • enumerable: true ensures it still appears in loops.

5️⃣ Looping Over Object Properties​

for (let [key, value] of Object.entries(chai)) {
  if (typeof value !== 'function') {
    console.log(`${key} : ${value}`);
  }
}
  • Object.entries(chai) returns an array of [key, value] pairs.
  • if (typeof value !== 'function') ensures orderChai() is skipped.
  • Since name is still enumerable, the output includes: 
    name : ginger chai
    price : 250
    isAvailable : true

📌 Key Takeaways​

✅ Object.getOwnPropertyDescriptor() helps inspect properties' attributes like writable, enumerable, and configurable.

✅ Object.defineProperty() allows modifying descriptors to control object behavior.

✅ Trying to modify Math.PI fails because writable: false.

✅ Looping through object properties excludes functions, demonstrating a way to filter values.