? JavaScript Object Properties

In JavaScript, object properties are key-value pairs that define the characteristics and data of an object. They are fundamental to how objects work.

?? Declaring Object Properties

let person = {  firstName: "Alice",  lastName: "Johnson",  age: 30};

• firstName, lastName, and age are property keys

• "Alice", "Johnson", and 30 are the property values

? Accessing Properties

Dot Notation

console.log(person.firstName); // "Alice"

Bracket Notation (useful for dynamic or invalid keys)

console.log(person["lastName"]); // "Johnson"let key = "age";console.log(person[key]); // 30

? Modifying Properties

person.age = 31;person["firstName"] = "Eve";

? Adding New Properties

person.email = "eve@example.com";

? Deleting Properties

delete person.lastName;

? Check If Property Exists

"age" in person;                  // trueperson.hasOwnProperty("email");  // true

? Looping Through Properties

for (let key in person) {  console.log(key + ": " + person[key]);}

? Property Names

• Can be strings or symbols

• If a property name has spaces or special characters, use quotes:

let obj = { "full name": "Alice Johnson" };console.log(obj["full name"]); // "Alice Johnson"

?? Object.defineProperty()

Advanced way to define a property with specific attributes:

let user = {};Object.defineProperty(user, "id", {  value: 101,  writable: false,  enumerable: true});console.log(user.id); // 101user.id = 202;        // won't change because writable is false

? Summary

• Object properties are key-value pairs.

• Access with dot or bracket notation.

• Modify, add, delete, and loop through them easily.

• Use hasOwnProperty() or in to check existence.

• Use defineProperty() for detailed control.

Would you like an example that builds a dynamic object from user input or JSON?