TypeScript

JavaScript, with a safety net

TypeScript adds a powerful type system to JavaScript: fewer bugs, better tooling and stress-free refactoring. From basic annotations to generics, narrowing and advanced utility types.

Foundations

Beginner - the basics, step by step

• Why TypeScript, your first typed fileDiscover what TypeScript is, the problem it solves, and write your very first typed file.
• Primitive types, arrays and simple unionsLearn the three basic types, how to type an array, and how to create type unions.
• Objects and interfacesDescribe the shape of your objects with precise types, then make them reusable with interfaces.
• Typing functions: parameters, return, optionalsMake your functions safer by typing their parameters, their return value and their optional parameters.
• Inference, any and unknownLet TypeScript figure out types with inference, and understand why unknown beats the dangerous any.

Progression

Intermediate - build real things

• type vs interface: extends and intersectionPick the right construct to model and compose your object types without duplicating code.
• Literal types and discriminated unionsModel your application's states with unions the compiler checks on your behalf.
• Enums and const assertions: the modern alternativesUnderstand the limits of enums and derive your types from frozen constants with as const.
• Generics: simple generic functions and typesWrite reusable functions and types that keep full type precision on every call.
• Typing real-world code: DOM, fetch, JSONKeep reliable types at your application's boundaries, where the DOM, the network, and JSON escape the compiler.

Advanced

Proficient - advanced patterns and performance

• Narrowing: typeof, in, instanceof, and type guardsYou master type narrowing mechanisms and write your own predicates to make unions more reliable.
• Advanced generics: constraints and defaultsYou constrain your type parameters with extends and provide defaults to build ergonomic generic APIs.
• Utility types: Partial, Pick, Omit, Record, ReturnTypeYou derive types from a single source with the built-in utilities to eliminate duplication and the drift it causes.
• never, exhaustiveness, and advanced discriminated unionsYou model your states with discriminated unions and lock in their exhaustiveness with the never type.
• Strict tsconfig: key options and common errorsYou understand what strict mode actually enables and know how to handle the typical errors it reveals in an existing project.

Mastery

Expert - architecture, internals and edge cases

• Conditional types and infer: the compiler's logicMaster the distributivity of conditional types, pattern matching with infer, and edge cases like never, any, and boolean.
• Mapped types and key remapping: transforming typesUnderstand how homomorphic mapped types preserve modifiers and how the as clause renames or filters keys.
• Template literal types: strings computed at compile timeLeverage template literal types to generate unions through Cartesian products and parse string literals with infer.
• Overloads, typed this, and varianceUnderstand overload resolution, the this pseudo-parameter, and the variance rules that govern function assignability.
• Production patterns: branded types, satisfies, and .d.tsApply the expert patterns that secure a real codebase: simulated nominality, validation without widening, and ambient declarations.