Arrays & Objects in JavaScript

📘 Arrays & Objects in JavaScript

Arrays and Objects are the two most important data structures in JavaScript. Let’s break them down clearly with examples and a mini project.

🔹 Arrays

An array is an ordered collection of values stored in a single variable. Arrays can hold numbers, strings, objects, or even other arrays.

✅ Example: Creating an Array

let fruits = ["apple", "banana", "cherry"];
console.log(fruits[0]); // apple
console.log(fruits[2]); // cherry
    

• Arrays are ordered collections, indexed from 0.
• Array lielements can be any type: primitives, objects, other arrays, functions.
• Arrays are reference types — assigning copies the reference, not the values.

Property: length, fruits.length // 3

length returns the number of elements in the array (always integer ≥ 0) Note: setting length can truncate or expand (with empty slots)

Iterating / common methods:

      fruits.forEach(f => console.log(f));
      let upper = fruits.map(f => f.toUpperCase());
      let bananas = fruits.filter(f => f === 'banana');

map/filter/reduce are functional-style helpers that return new arrays/values.

🔧 Common Array Methods

let numbers = [10, 20, 30];

// Add elements
numbers.push(40); // [10,20,30,40]

// Remove last element
numbers.pop();    // [10,20,30]

// Remove first element
numbers.shift();  // [20,30]

// Add element at beginning
numbers.unshift(5); // [5,20,30]

// Loop through array
numbers.forEach(num => console.log(num));
    

🔹 Objects

An object is a collection of key–value pairs. Keys are strings (or Symbols), and values can be any data type.

✅ Example: Creating an Object

let user = {
  name: "Alice",
  age: 25,
  isStudent: true
};

console.log(user.name);  // Alice
console.log(user["age"]); // 25
    

🔧 Adding / Updating / Deleting Properties

user.country = "USA";    // add
user.age = 26;           // update
delete user.isStudent;   // delete
console.log(user);
    

🌍 Combining Arrays & Objects

Often, we combine arrays and objects to represent structured data.

// Array of objects
let users = [
  { name: "Alice", age: 25 },
  { name: "Bob", age: 30 }
];

console.log(users[1].name); // Bob

// Object with array property
let classroom = {
  teacher: "Mr. Smith",
  students: ["Alice", "Bob", "Charlie"]
};

console.log(classroom.students[2]); // Charlie
    

4️⃣ Mini Project: Simple Contact List

const contacts = [
  { name: "Rahul", phone: "9876543210" },
  { name: "Priya", phone: "9123456780" },
  { name: "Amit", phone: "9988776655" }
];

// Add a new contact
contacts.push({ name: "Sneha", phone: "9001122334" });

// Find a contact by name
function findContact(name) {
  return contacts.find(contact => contact.name === name);
}

console.log(findContact("Priya")); 
// { name: "Priya", phone: "9123456780" }
  

🔑 Key Points

• Use arrays for ordered collections of items.
• Use objects for structured data with named properties.
• You can nest arrays inside objects and vice versa.
• Both arrays and objects are reference types in JavaScript.