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TypeScript

682 problems50 sections📅 2026 curriculum

Learn TypeScript by typing real, typed code.

Practice the parts of TypeScript that trip people up: interfaces vs. types, generics, discriminated unions, and how the compiler narrows a type through your control flow. You type genuine, well-typed snippets and an AI tutor unpacks each line — what a mapped type does, why an assertion is a smell — so the type system stops fighting you and starts helping.

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Run TypeScript on your machine

1. Install the toolchain

npm i -g typescript tsx

2. Save your code as hello.ts, then compile & run

npx tsx hello.ts # or: tsc hello.ts && node hello.js

Official install docs ↗

progress by section

1Fundamentals0/5start →

Typed bindings Functions and arrows Control flow Literal union types as const inference

2Strings In Depth0/18start →

Case and trimming Strings are immutable Repeat The string type Search a string Pad to a width Replace text split and join Trim one side Character with at()Typed helper Compare for sorting Convert to and from numbers Iterate characters Slice a substring Match a pattern Template literal types Template types over unions

3Values & References0/18start →

Aliasing Copy an array const blocks rebinding Reference identity Primitives are safe readonly properties Value vs reference Mutation via reference readonly parameter Readonly<T>Reassigning a parameter Shallow copy const assertions Object.freeze Freeze is shallow Return new vs mutate Shallow copy shares nested structuredClone

4Slices & Arrays0/18Unlock →

Arrays Membership Safe access with at()Destructuring with types Fill Reverse a copy Slice a range Sort without mutating Spread Tuple types Find an index or element Flatten and concat Labeled tuple return Readonly tuples Sort by a key Chunk into groups Sliding windows Immutable update and splice

5Data structures0/8Unlock →

Typed arrays Record lookup Tuples Interface for a struct Map word count Readonly arrays Set dedup A generic stack

6Iterators0/20Unlock →

7Traits0/21Unlock →

8Generics0/20Unlock →

9Lifetimes0/20Unlock →

10Closures0/20Unlock →

11Pattern Matching0/20Unlock →

12Error Handling0/20Unlock →

13Option & Result0/20Unlock →

14Conversions0/15Unlock →

Value to String String to characters Boolean as a number Value to boolean Char and code point String to number parseInt with a radix Number to another base Unary plus Array.from an iterable Type assertion with as Array to a typed tuple JSON.parse with a cast as vs satisfies Parse with a template literal type

15Collection Conversions0/19Unlock →

Array to Set Unique and sorted flat and flatMap Map keys to array Map values to array Iterate object entries Pairs to a Map Set to sorted array as const tuples Frequency Map Map keys to a Set Map to pairs Map to Object Build an object from pairs Object to Map Two arrays to a Map Unique, keeping order Group into a Map Invert a Record

16Math0/14Unlock →

min, max, clamp Math constants Factorial Roots and powers Integer arithmetic Rounding Logarithms and exp Trigonometry GCD and LCM hypot and atan2 Prime test Non-negative modulo Safe integers and bigint Mean, median, stdev

17Encoding0/22Unlock →

18Random0/20Unlock →

19Data I/O0/18Unlock →

Parse CSV into rows Tab-separated values Build a CSV string Select one column CSV into a number matrix Split off the header Typed JSON parse Whitespace-separated matrix Read a data file Serialize records to CSV Skip blanks and comments Print an aligned table Write CSV to a file Append a row key=value into a Map key=value into a Record Round-trip write then read Drop unparseable rows

20Linear Algebra0/21Unlock →

21Text Processing0/16Unlock →

Trim whitespace Word count Capitalize the first letter Count occurrences Pad and align Replace text Reverse a string Reverse word order Strip all whitespace Count vowels Character frequency Longest word Number the lines Title case Truncate with an ellipsis Levenshtein distance

22Date & Time0/12Unlock →

Current date and time Date components Build a Date Add days Days between dates UNIX timestamp ISO 8601 format Time a block of work Seconds to H:M:S Parse a datetime Format in a timezone Parse a clock string

23Memory0/12Unlock →

References vs copies Swap without a temp Object.freeze Object.is Readonly<T>structuredClone const assertions Shallow vs deep copy A typed array WeakMap for side data ArrayBuffer and DataView A DeepReadonly type

24Modules0/20Unlock →

25Macros0/20Unlock →

26Testing0/20Unlock →

27Algorithms0/8Unlock →

Greatest common divisor Binary search Palindrome check Fibonacci with memoization Merge two sorted arrays Shuffle with an LCG Two sum Partition and quicksort

28Sorting Algorithms0/12Unlock →

Array.sort with a comparator Check if sorted Bubble sort Sort by a key Insertion sort Selection sort Counting sort Merge sort Shell sort Heapsort Quicksort Radix sort

29Expression Parsing0/6Unlock →

Evaluate postfix (RPN)Tokenize an expression Evaluate infix Recursive-descent calculator Right-associative power Shunting-yard

30Idioms0/9Unlock →

const assertions Typed destructuring Optional chaining readonly satisfies operator Type guards Utility types Discriminated unions Template literal types

31OOP & Traits0/8Unlock →

Encapsulation Implements an interface Abstract class Getters and setters Extends and super Parameter properties Static members Polymorphism

32Trait Objects0/14Unlock →

An interface-typed array Default method over an interface Factory returning an interface Narrowing dispatch Take an interface parameter A shared reference Discriminated union An extended interface An array of functions Return an Iterable Recover the concrete type Polymorphism via interface A read-only view A handler registry

33Design Patterns0/14Unlock →

Prototype Singleton Adapter Builder Factory Method Lazy Initialization Observer Strategy Command Decorator State Dependency Injection Object Pool Actor

34Async0/3Unlock →

async/await and sleep Promise combinators Async generators and abort

35File I/O0/6Unlock →

Read a file Write a file Append to a file Count lines Temp-file round-trip Async file I/O

36Filesystem0/18Unlock →

Does a path exist?Copy a file Build a path Create nested directories List a directory Rename or move Files vs directories Path components Remove a tree Sorted listing File metadata Write to the temp dir Change the extension Filter by extension Last modified time Absolute path Total size of a tree Walk the tree

37Networking0/16Unlock →

Parse the request line Route by path Classify an IP address Parse a socket address Bind an ephemeral port Build an HTTP response An HTTP server Read lines from a stream Resolve a hostname Shut down a connection TCP client Read timeout UDP receive UDP send Per-connection handling TCP echo server

38Concurrency0/7Unlock →

Sequencing with async/await Run tasks with Promise.all race, any and allSettled A typed async queue A typed async mutex A worker thread Atomics over shared memory

39Unsafe & FFI0/14Unlock →

A Node Buffer A Float64Array An Int32Array view A typed array Buffer endianness Bit-level byte manipulation Aliased views (a union)A NUL-terminated string DataView endianness SharedArrayBuffer A shared subarray Atomic byte operations Reinterpret float bits Transfer with structuredClone

40Commands0/14Unlock →

Command-line arguments Skip node and the script Env var with a default Read an environment variable Current directory Iterate all env vars Set and remove a variable Path to this executable Exit with a code This module's URL Pass env to a child Run a command Command exit status Read all of stdin

41Array0/10Unlock →

Contains Duplicate Two Sum Best Time to Buy and Sell Stock Maximum Subarray Container With Most Water Find Minimum in Rotated Sorted Array Product of Array Except Self Maximum Product Subarray Search in Rotated Sorted Array 3Sum

42Binary0/5Unlock →

Missing Number Number of 1 Bits Counting Bits Reverse Bits Sum of Two Integers

43String0/10Unlock →

Valid Anagram Valid Palindrome Valid Parentheses Encode and Decode Strings Group Anagrams Longest Substring Without Repeating Characters Longest Repeating Character Replacement Longest Palindromic Substring Palindromic Substrings Minimum Window Substring

44Matrix0/4Unlock →

Rotate Image Set Matrix Zeroes Spiral Matrix Word Search

45Interval0/5Unlock →

Meeting Rooms Merge Intervals Insert Interval Non-overlapping Intervals Meeting Rooms II

46Linked List0/6Unlock →

Reverse Linked List Linked List Cycle Merge Two Sorted Lists Remove Nth Node From End Merge K Sorted Lists Reorder List

47Tree0/14Unlock →

Maximum Depth of Binary Tree Invert Binary Tree Same Tree Lowest Common Ancestor of a BST Binary Tree Level Order Traversal Subtree of Another Tree Implement Trie (Prefix Tree)Kth Smallest Element in a BST Validate Binary Search Tree Add and Search Word Construct Binary Tree from Preorder and Inorder Binary Tree Maximum Path Sum Serialize and Deserialize Binary Tree Word Search II

48Graph0/8Unlock →

Number of Connected Components Number of Islands Clone Graph Course Schedule Longest Consecutive Sequence Graph Valid Tree Alien Dictionary Pacific Atlantic Water Flow

49Heap0/3Unlock →

Kth Largest Element in an Array Top K Frequent Elements Find Median from Data Stream

50Dynamic Programming0/11Unlock →

Climbing Stairs House Robber Unique Paths Coin Change House Robber II Jump Game Combination Sum IV Decode Ways Longest Common Subsequence Longest Increasing Subsequence Word Break