Objects: Operations and Utility Methods

In JavaScript, almost everything is an object. An object is a collection of related data or functionality in the form of key-value pairs (properties and methods).

1. Creating Objects & Property Access

Objects are typically created using object literal syntax {}:

const car = {
  make: "Toyota",
  model: "Corolla",
  year: 2022,
  start: function() {
    console.log("Engine started.");
  }
};

Accessing Properties:

You can read values using Dot Notation or Bracket Notation:

// Dot Notation
console.log(car.make); // "Toyota"

// Bracket Notation (Required when property keys contain spaces or are dynamic variables)
console.log(car["model"]); // "Corolla"

let key = "year";
console.log(car[key]); // 2022

2. Managing Properties (CRUD)

Properties in JavaScript objects can be added, updated, or deleted dynamically:

const user = { name: "Alice" };

// 1. Create / Update
user.age = 25;        // Adds new property 'age'
user.name = "Bob";    // Updates existing property 'name'

// 2. Delete
delete user.age;      // Removes property 'age'
console.log(user);    // { name: "Bob" }

3. Useful Object Methods

JavaScript provides a global Object constructor with utility methods to inspect and manipulate objects.

A. Extracting Keys, Values, and Entries

• Object.keys(obj): Returns an array of an object's keys (property names).
• Object.values(obj): Returns an array of an object's values.
• Object.entries(obj): Returns an array of an object's [key, value] pairs.

const user = { name: "Alice", age: 25 };

console.log(Object.keys(user));    // ["name", "age"]
console.log(Object.values(user));  // ["Alice", 25]
console.log(Object.entries(user)); // [["name", "Alice"], ["age", 25]]

B. Cloning and Merging: Object.assign()

Copies properties from source objects to a target object.

const defaultSettings = { theme: "light", showSidebar: true };
const userSettings = { theme: "dark" };

// Merge settings into a new object:
const settings = Object.assign({}, defaultSettings, userSettings);
console.log(settings); // { theme: "dark", showSidebar: true }

C. Immutability: freeze() and seal()

• Object.seal(obj): Prevents adding or deleting properties. Existing properties can still be updated.
• Object.freeze(obj): Makes an object completely read-only. Prevents adding, deleting, or editing properties.

const config = { apiEndpoint: "https://api.example.com" };
Object.freeze(config);

config.apiEndpoint = "https://hacked.com"; // Ignored in normal mode, throws Error in strict mode
console.log(config.apiEndpoint); // "https://api.example.com"

In the next guide, we will cover array operations and modern functional array methods like map, filter, and reduce.