JavaScript Arrays and Objects

JavaScript Arrays

// Create
const fruits = ["apple", "banana", "cherry"];
const mixed = [1, "two", true, null, { id: 1 }];

// Access
console.log(fruits[0]);    // apple
console.log(fruits.length); // 3

// Modify
fruits.push("date");        // add at end
fruits.unshift("avocado");  // add at start
const last = fruits.pop();  // remove from end
const first = fruits.shift(); // remove from start
fruits.splice(1, 1, "mango"); // remove/insert at index

Array Methods

const nums = [1, 2, 3, 4, 5];

// map — transform elements
const doubled = nums.map(n => n * 2);   // [2,4,6,8,10]

// filter — select elements
const evens = nums.filter(n => n % 2 === 0);  // [2,4]

// reduce — accumulate
const sum = nums.reduce((acc, n) => acc + n, 0);  // 15

// find / findIndex
const found = nums.find(n => n > 3);       // 4
const idx = nums.findIndex(n => n > 3);   // 3

// some / every
nums.some(n => n > 4);   // true
nums.every(n => n > 0);  // true

// includes
nums.includes(3);  // true

// sort
["banana","apple","cherry"].sort(); // alphabetical
nums.sort((a, b) => a - b);         // ascending numeric

// flat / flatMap
[[1,2],[3,4]].flat();               // [1,2,3,4]

// forEach (no return value)
nums.forEach(n => console.log(n));

// Spread operator
const copy = [...nums];
const combined = [...nums, 6, 7];

JavaScript Objects

// Object literal
const person = {
    name: "Alice",
    age: 25,
    address: {
        city: "Delhi",
        pin: "110001"
    },
    greet() {
        return `Hi, I'm ${this.name}`;
    }
};

// Access
console.log(person.name);           // dot notation
console.log(person["age"]);         // bracket notation
console.log(person.address.city);   // nested access
console.log(person.greet());        // method call

// Modify
person.age = 26;
person.email = "alice@email.com";   // add property
delete person.email;                // delete property

Object Methods

Object.keys(person);    // ["name","age","address"]
Object.values(person);  // ["Alice", 25, {...}]
Object.entries(person); // [["name","Alice"], ...]

// Spread and merge
const updated = { ...person, age: 27 };

// Destructuring
const { name, age } = person;
const { address: { city } } = person;

Array vs Object

Key Takeaway: Arrays (ordered lists) and Objects (key-value maps) are the core data structures in JavaScript. Master array methods like map, filter, reduce and object destructuring for clean, functional code.