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Learning paths

JavaScript developer
TypeScript application developer
Python problem solver
SQL reporting engineer
React application developer
Go developer
Java developer
Rust developer
.NET backend developer
Next.js application developer
Node.js backend developer
Python web developer

Courses and lessons

JavaScript from zero

Your first instruction
Give values a name
Calculate a total
Choose a path
Read and fix an error
Reuse a function
Keep an ordered list
Repeat with a loop
Select matching items
Describe a real thing
Project · Expense summary

Python from zero

Your first instruction
Give values a name
Calculate a total
Choose a path
Read and fix an error
Reuse a function
Keep an ordered list
Repeat with a loop
Select matching items
Describe a real thing
Project · Expense summary

SQL for everyday data

Read a table
Filter rows
Sort deliberately
Aggregate a result
Group related rows
Filter groups
Connect related data
Project · Spending report

TypeScript after JavaScript

Describe a value
Type a function
Describe an object
Narrow a union
Keep a type relationship
Project · Typed expense summary

SQL from tables to your first report

Read a table before writing a query
Keep matching rows with WHERE
Combine conditions without guessing precedence
Understand unknown values and NULL
Sort ties and choose a small result
Count rows before grouping them
Build a grouped report and filter groups
Project · Join learners to enrollment counts

React from your first component

Set up and render your first component
Reuse a component with props
Respond to a click with state
Make an input and a form work together
Render a list and an empty state
Share state between two components
Use an effect only for an external system
Project · Build a filterable reading list

Node.js from a script to an API

Run a JavaScript file outside the browser
Understand imports and explicit exports
Wait for a promise without blocking JavaScript
Read and validate a JSON file
Receive an HTTP request and return JSON
Validate a query parameter at the boundary
Write repeatable tests for the logic
Project · A small searchable topics API

Go · From values to tested services

Values, functions and explicit returns
Loops, slices and shared storage
Structs, maps and missing values
Errors and input boundaries
Goroutines and channel ownership
Project · Validate and summarize expenses

Java · From methods to reliable programs

Types, methods and conditions
Lists, loops and independent results
Records and value-oriented modeling
Parsing and exception boundaries
Streams and grouping without mutation
Project · Inventory with checked updates

Rust · Ownership, errors and useful programs

Bindings, expressions and functions
Borrow strings instead of moving them
Enums and exhaustive decisions
Result and error propagation
Iterators, vectors and map entries
Project · A checked expense total

C# · From expressions to async programs

Types, expressions and methods
Collections, loops and LINQ
Records, nullable values and validation
TryParse and expected failures
Async, await and cancellation
Project · A tested expense report

React · Build a working foundation

Components, props and composition
Events, state snapshots and updates
Stable keys and immutable list changes
Controlled forms and useful validation
Derived state and searchable lists
Project · A timer with reliable cleanup

Next.js · Build a working foundation

Routes, layouts and internal links
Dynamic routes and missing resources
Server and Client Component boundaries
Route handlers and validated input
Loading states and recoverable errors
Project · A public course page with accurate metadata

Node.js · Build a working foundation

Modules and validated configuration
Files, paths and resource boundaries
Streams and backpressure
Sequential awaits and bounded concurrency
HTTP routing and explicit responses
Project · Test a service contract

Express / NestJS · Build a working foundation

Express routing and middleware order
Bounded bodies and runtime validation
Express async failures and final error handling
Nest modules, controllers and providers
Nest DTOs and validation pipes
Project · Pagination with a stable contract

Django / FastAPI · Build a working foundation

Django URL patterns and views
Django models and database constraints
Django forms, CSRF and server validation
FastAPI request and response models
FastAPI dependencies and cleanup
Project · Test API behavior through HTTP

ASP.NET Core · Build a working foundation

Minimal APIs and typed route inputs
Dependency injection and service lifetimes
DTO validation at an API boundary
Authentication and authorization are different checks
Cancellation and safe error responses
Project · An API with integration tests

JavaScript · Algorithm practice lab

Validate nested brackets with a stack
Answer range totals with prefix sums
Count peak overlap with event ordering
Dynamic programming with a rolling state

TypeScript · Model reliable updates

Transform a discriminated result safely
Distinguish missing fields from falsy values
Sort records with a deterministic tie-breaker
Apply commands through an explicit state machine

Python · Iterators and efficient searches

Consume a generator without losing order
Merge sorted streams with a heap
Count target-sum subarrays
Locate insertion boundaries with bisect

SQL · Explainable analytical reports

Conditional aggregation in one grouped report
Compare each event with its predecessor
Select one representative from each duplicate group
Calculate category shares with an explicit denominator

JavaScript engineering patterns

Project · A bounded LRU cache
Order jobs and detect dependency cycles
Preserve outcomes across asynchronous failures
Find the longest unique-character window

TypeScript at application boundaries

Validate untrusted JSON at the boundary
Model legal state transitions
Keep generic grouping type safe

Python data pipelines and algorithms

Merge overlapping reservations
Rank frequent events with a bounded heap
Project · Parse a stream of event records

SQL beyond basic queries

Keep every row tied for first place
Make running totals deterministic
Project · Paginate a changing activity feed

Go · Cancellation in a bounded worker pool

Go · Cancellation in a bounded worker pool

Rust · Share ownership without hiding failures

Rust · Share ownership without hiding failures

Java · Coalesce concurrent cache loads

Java · Coalesce concurrent cache loads

C# · Bound asynchronous work and propagate cancellation

C# · Bound asynchronous work and propagate cancellation

React · Prevent stale requests from replacing current state

React · Prevent stale requests from replacing current state

Node.js · Stream files with backpressure

Node.js · Stream files with backpressure

Next.js · Authorize every server-side mutation

Next.js · Authorize every server-side mutation

Express / NestJS · Design an idempotent write

Express / NestJS · Design an idempotent write

Django / FastAPI · Keep blocking work out of async handlers

Django / FastAPI · Keep blocking work out of async handlers

ASP.NET Core · Detect conflicting edits with a version token

ASP.NET Core · Detect conflicting edits with a version token

System design · Deliver events with a transactional outbox

System design · Deliver events with a transactional outbox

Database engineering · Transfer value without lost updates

Database engineering · Transfer value without lost updates

DevOps / Cloud · Drain a service during deployment

DevOps / Cloud · Drain a service during deployment

JavaScript: dependable data and services

Aggregate without mutating the input
Find the first matching value with binary search
Plan bounded retries
Project · Apply each ledger event once

TypeScript: runtime contracts and generics

Return a typed validation result
Preserve types while batching work

Python: reliable collections and imports

Remove duplicates while preserving order
Find a shortest path through an unweighted graph
Project · Validate an entire import before applying it

SQL: trustworthy customer reports

Find missing relationships safely with NOT EXISTS
Project · Report on customers with no orders

React: an expense application lab

Model expense transitions with a reducer
Make input errors understandable
Project · Handle stale requests and failed responses

Interview questions

Two Sum
Valid Parentheses
Remove Duplicate Values
Explain the Event Loop
Model API States with Unions
Generators vs. Lists
Async, Await & Cancellation
Design a Bounded Worker Pool
Equals and HashCode Contract
Ownership Across Threads
Diagnose a Slow SQL Query
Design a URL Shortener
Handle a Cache Stampede
Debug a Latency Regression
Find the longest unique-character window
Validate untrusted JSON at the boundary
Rank frequent events with a bounded heap
Keep every row tied for first place
Binary Search · Find a Sorted Value
Palindrome · Compare from Both Ends
Best Single Buy and Sell
Longest Substring without Repeats
Count Subarrays with a Target Sum
Merge Overlapping Intervals
Days until a Warmer Temperature
Maximum Depth of a Binary Tree
Shortest Path in an Unweighted Graph
Fewest Coins for an Amount
Reverse a Singly Linked List
Trapping Rain Water

Guides

TypeScript unknown vs any: validate an API response
Why LEFT JOIN and COUNT(*) can report one order for a new customer
Handle a retried API write without applying it twice
ROW_NUMBER, RANK and DENSE_RANK: choose a tie policy
TypeScript में unknown और any: API से आए डेटा की जाँच
SQL LEFT JOIN के साथ COUNT(*) गलत गिनती क्यों दिखा सकता है?

Tools

Big-O growth explorer
SQL practice and query-plan lab
System-design capacity calculator

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