TypeScript for JavaScript Developers

TypeScript is JavaScript with a compile-time type system — the language you already know, plus a checker that catches bug categories before they ship. This track starts from your existing JavaScript fluency: every lesson explains why the type system exists, shows the plain-JS failure pattern it prevents, and teaches the production practices that make types pay off in real codebases. You keep the entire JavaScript ecosystem; you gain refactor safety, self-documenting APIs, and a CI gate for correctness.

How to study this track: lessons build in order — the compiler model from phase 1 is assumed everywhere else. Each example states its purpose, the output you should see, and the takeaway; run the demos locally as you go.

TypeScript Study Progress

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#	TypeScript	Topic	Description
PHASE 1: WHY TYPESCRIPT & FOUNDATIONS
	01	Why TypeScript for JavaScript Developers	The runtime-bug patterns types eliminate, what TypeScript changes and what it deliberately does not.
	02	Setup and the Strict Toolchain	Install tsc as a project tool, a strict tsconfig baseline, and the three ways to run TypeScript.
	03	Inside the Compiler	Checking versus emitting, type erasure, and disciplined error suppression.
	04	The Syntax Delta	Annotation syntax and the type-level constructs layered onto JavaScript you already know.
PHASE 2: THE TYPE SYSTEM
	05	Core Types and Narrowing	Primitives, any versus unknown, unions, discriminated unions, and control-flow narrowing.
	06	Structural Typing	Why shapes, not names, decide compatibility — and when that backfires.
	07	Typed Functions	Signatures, overloads, contextual typing, and safe callbacks.
	08	Interfaces and Contracts	Optional and readonly members, interface versus type alias, declaration merging.
	09	Classes and Invariants	Access modifiers, strict initialization, and composition over inheritance.
	10	Generics and Inference	Type parameters, constraints, and designing for inference first.
PHASE 3: ADVANCED TYPE PROGRAMMING
	11	Mapped and Conditional Types	Computing new types from existing ones: key remapping, `infer`, template literals.
	12	Declaration Files and Augmentation	Reading and writing `.d.ts`, `@types` packages, safe module augmentation.
	13	Modules and Imports	ESM versus CommonJS, `verbatimModuleSyntax`, resolution and barrel files.
	14	Decorators and Metadata	Stage 3 versus legacy decorators, metadata patterns, when the trade-off pays.
PHASE 4: PRODUCTION
	15	Errors and Runtime Validation	`unknown` catches, result types, and validating untrusted data with zod.
	16	Testing TypeScript	What types prove versus what tests prove; typing Vitest suites and mocks.
	17	Linting, Formatting, CI	typescript-eslint, project references, and the incremental CI pipeline.
	18	Run and Debug	Source maps, launch configs, and debugging compiled output.
	19	Migrating JavaScript to TypeScript	The strangler-fig path: allowJs, JSDoc checking, gradual strictness.
	20	Framework Integration	React, Node APIs, and library authoring with typed boundaries.
	21	Architecture at Scale	Type layers, project references, and keeping the checker fast in monorepos.
PHASE 5: PRACTICE & DEMO
	22	Demo Examples Lab	Runnable single-file TypeScript demos with source and live preview.
	23	Study Projects	Progressive projects that apply every phase of the track.
	24	Open-Source Lab	TypeScript repositories on GitHub worth studying, with what to read in each.
PHASE 6: REFERENCE
	25	References and Standards	Official documentation, free books and courses, tooling references.

Free TypeScript Resources

Resource	What it is
typescriptlang.org/docs	The official handbook and reference — the primary source this track cites.
TypeScript Playground	Run and share TypeScript in the browser; test every example without installing anything.
Total TypeScript Tutorials	Matt Pocock's free tutorials, from beginner exercises to type-level wizardry.
typescript-eslint	The official linting layer for TypeScript-specific rules.
TSConfig Reference	Every compiler option, explained by the team that built them.
TypeScript Tooling cheatsheets	Community-maintained cheatsheets for real-world setups.