Every property in an object has hidden settings:

Whether its value can be changed (writable),

Whether it shows up during enumeration (enumerable),

Whether it can be deleted or reconfigured (configurable).

These settings are called property descriptors.

Getting a Property Descriptor

Use: getOwnPropertyDescriptor(obj, prop).

Example with Mia:

const mia = {
  name: 'Mia',
  age: 23
};

let descriptor = Object.getOwnPropertyDescriptor(mia, 'age');
console.log(descriptor);

Defining a Property Descriptor

Use: defineProperty(obj, prop, descriptor).

Example with Eva:

const eva = {};

Object.defineProperty(eva, 'isCoder', {
  value: true,
  writable: false,
  enumerable: true,
  configurable: true
});

console.log(eva.isCoder); // true
eva.isCoder = false;
console.log(eva.isCoder); // still true!

Defining Multiple Properties: defineProperties()

Example with Elle:

const elle = {};

Object.defineProperties(elle, {
  city: {
    value: 'Paris',
    writable: true,
    enumerable: true
  },
  age: {
    value: 21,
    writable: false,
    enumerable: false
  }
});

console.log(elle.city); // Paris
console.log(elle.age);  // 21

Fun Tricks:

Hidden property:

Make a property invisible during enumeration enumerable: false

const anna = {};

Object.defineProperty(anna, 'secret', {
  value: 'I love coding',
  enumerable: false
});

console.log(Object.keys(anna)); // []
console.log(anna.secret); // "I love coding"

Immutable property:

Set writable: false to lock the value.

Protected structure:
Set configurable: false to prevent deleting the property.

Notes

writable: false locks a property’s value.

enumerable: false hides a property during loops.

configurable: false makes a property undeletable and its settings permanent.

Mastering property descriptors gives you fine-grained control over how objects behave and interact in your applications.