Top 5 Data Structures in JavaScript

Let’s go through the Top 5 Data Structures in JavaScript — with explanations, use cases, and examples 👇

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🧩 1️⃣ Array

🔹 What it is:

An ordered collection of items — used for lists, stacks, queues, and heaps (via logic).

🔹 Key features:

• Indexed (starts from 0)
• Can store any data type (even mixed)
• Dynamic — grows/shrinks automatically

🔹 Example:

let numbers = [10, 20, 30];
numbers.push(40);       // Add at end
numbers.unshift(5);     // Add at start
numbers.pop();          // Remove from end
console.log(numbers);   // [5, 10, 20, 30]

🔹 Use cases:

• Sorting and searching
• Stack/Queue implementations
• Storing ordered lists (e.g., scores, logs)

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🪣 2️⃣ Object

🔹 What it is:

A key-value store — like a dictionary or hashmap.

🔹 Key features:

• Unordered (until ES6, insertion order now mostly preserved)
• Keys are strings or symbols
• Very fast lookups

🔹 Example:

let person = {
  name: "Alice",
  age: 25,
  city: "Sydney"
};

console.log(person.name); // Alice
person.job = "Engineer";  // Add new key
delete person.city;       // Remove key

🔹 Use cases:

• Representing structured data (like JSON)
• Storing configuration or mapping
• Caching key-value data

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🗺️ 3️⃣ Map

🔹 What it is:

A modern key-value store introduced in ES6 — similar to an object, but with more power.

🔹 Key features:

• Keys can be any type (objects, numbers, functions)
• Maintains insertion order
• Has built-in iteration methods

🔹 Example:

let scores = new Map();
scores.set('Alice', 90);
scores.set('Bob', 85);
scores.set({id: 1}, 70);

console.log(scores.get('Alice')); // 90
console.log(scores.size);         // 3

🔹 Use cases:

• Caches or lookup tables
• Associating metadata with objects
• When you need guaranteed key order

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🧮 4️⃣ Set

🔹 What it is:

A collection of unique values — no duplicates allowed.

🔹 Key features:

• Automatically removes duplicates
• Supports fast membership checking

🔹 Example:

let numbers = new Set([1, 2, 3, 3, 4]);
numbers.add(5);
numbers.delete(2);

console.log(numbers);         // Set {1, 3, 4, 5}
console.log(numbers.has(3));  // true

🔹 Use cases:

• Removing duplicates from arrays

  let unique = [...new Set([1, 2, 2, 3, 3])];
  // [1, 2, 3]
  

• Tracking visited nodes in graphs

• Membership or uniqueness checks

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🪵 5️⃣ Stack / Queue (via Array)

🔹 What it is:

Arrays can simulate both these linear data structures easily.

Stack (LIFO):

let stack = [];
stack.push(10);
stack.push(20);
stack.pop();
console.log(stack); // [10]

Queue (FIFO):

let queue = [];
queue.push(10);
queue.push(20);
queue.shift();
console.log(queue); // [20]

🔹 Use cases:

• Function call management
• Undo/Redo operations
• BFS/DFS in graph traversal

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💡 Summary

Data Structure	Syntax	Best For
Array	[]	Ordered lists, stacks, queues
Object	{}	General key-value pairs
Map	new Map()	Complex keys, guaranteed order
Set	new Set()	Unique collections
Stack/Queue	via Array	Algorithmic tasks