Learn DSA in JavaScript from scratch

JavaScript suits learners who already build for the web and want to practise DSA without switching languages. Arrays, Map and Set are useful, but JavaScript has no built-in heap and its Number and sorting rules need special attention.

Open the JavaScript compiler Trace your code line by line Start the path

What you need from JavaScript before DSA

Variables and types

JavaScript variables can hold different values, and all ordinary numbers use the Number type.

const count = 3;
const label = "items";
console.log(label, count);

Output: items 3

Conditionals and loops

Scanning arrays and state machines depend on branches and iteration.

let total = 0;
for (const value of [2, 4, 5]) {
  if (value % 2 === 0) total += value;
}
console.log(total);

Output: 6

Functions

Functions keep an algorithm's inputs, output and local state together.

function double(value) {
  return value * 2;
}
console.log(double(6));

Output: 12

Recursion

Tree traversal and divide-and-conquer call the same function on smaller input.

function countdown(n) {
  if (n === 0) return;
  console.log(n);
  countdown(n - 1);
}
countdown(3);

Output: 3 2 1

Arrays and lists

Arrays provide indexed storage and are the base for stacks, queues and heaps.

const numbers = [3, 1, 2];
numbers.push(4);
console.log(numbers[1], numbers.length);

Output: 1 4

Strings

String indexing and slicing appear in parsing, matching and two-pointer problems.

const word = "level";
console.log(word === [...word].reverse().join(""));

Output: true

Hash maps and sets

Map and Set give direct membership and frequency operations without converting keys to strings.

const seen = new Set([2, 4]);
const counts = new Map([["a", 2]]);
console.log(seen.has(4), counts.get("a"));

Output: true 2

References and copying

Array assignment shares the same object; use a shallow or deep copy intentionally.

const first = [1, 2];
const second = [...first, 3];
console.log(first, second);

Output: [ 1, 2 ] [ 1, 2, 3 ]

Classes or structs

A class can model a linked-list or tree node with fields and references.

class Node {
  constructor(value) { this.value = value; }
}
console.log(new Node(7).value);

Output: 7

Sorting with a custom comparator

Array.sort needs an explicit numeric comparator for algorithmic ordering.

const items = [["b", 2], ["a", 1]];
items.sort((a, b) => a[1] - b[1]);
console.log(items);

Output: [ [ 'a', 1 ], [ 'b', 2 ] ]

Reading input

Browser exercises often provide a string, while judge runners expose input through a platform-specific harness.

const input = "2 4";
const values = input.trim().split(/\s+/).map(Number);
console.log(values[0] + values[1]);

Output: 6

JavaScript toolbox for data structures

Structure	JavaScript type	Key operations
Dynamic array	Array	push/pop at end; indexing O(1)
String building	Array + join	push pieces, then join once
Hash map	Map	get/set, any key, insertion order
Hash set	Set	add/has, any value, insertion order
Stack	Array	push/pop at the end
Queue	Array + head index	push at end, read then advance head
Deque	Array	push/pop at end; avoid shift/unshift
Priority queue	None built in	implement a binary heap or use a library
Ordered map	None built in	use sorted arrays or a library
Sorting	Array.sort	pass (a, b) => a - b for numbers

The order to learn DSA

Follow the SDE roadmap order. Each topic starts with two Easy problems from the curated set.