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Learning paths

JavaScript developer
TypeScript application developer
Python problem solver
SQL reporting engineer
React application 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

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

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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