Data Types and Structures

Data Types and Structures

Node.js uses JavaScript's data types. Some are primitives, some are objects. Let me walk you through what you will use.

Primitive Types

// String
const name = "Alice";
const greeting = `Hello, ${name}!`;  // Template literal

// Number
const age = 25;
const price = 9.99;
const huge = 9007199254740991;  // Max safe integer

// Boolean
const isActive = true;

// Null and Undefined
const nothing = null;      // Intentionally empty
let notDefined;            // undefined

// Symbol (unique identifier)
const id = Symbol("id");

// BigInt (for very large numbers)
const big = 9007199254740991n;

Objects

Objects store data as key-value pairs:

const user = {
  name: "Alice",
  age: 30,
  email: "alice@example.com",
  greet() {
    return `Hi, I am ${this.name}`;
  }
};

console.log(user.name);      // Alice
console.log(user.greet());   // Hi, I am Alice

// Add new property
user.phone = "555-1234";

// Delete property
delete user.email;

Arrays

Arrays are ordered lists. Node.js gives you powerful array methods:

const fruits = ["apple", "banana", "cherry"];

// Add and remove
fruits.push("date");        // Add to end
fruits.pop();               // Remove from end
fruits.unshift("avocado");  // Add to beginning
fruits.shift();             // Remove from beginning

// Find and filter
const long = fruits.filter(f => f.length > 5);
const upper = fruits.map(f => f.toUpperCase());
const hasBanana = fruits.includes("banana");

// Sort
const sorted = [...fruits].sort();

Destructuring

Extract values from objects and arrays cleanly:

// Object destructuring
const { name, age, ...rest } = user;

// Array destructuring
const [first, second, ...others] = fruits;

// In function parameters
function greet({ name, age }) {
  return `${name} is ${age}`;
}

Map and Set

These are built-in data structures for specific use cases:

// Map - key-value pairs with any key type
const cache = new Map();
cache.set("user:1", { name: "Alice" });
cache.get("user:1");
cache.has("user:1");
cache.size;

// Set - unique values
const unique = new Set([1, 2, 2, 3, 3]);
unique.size;  // 3
unique.add(4);
unique.delete(1);