Typescript terms
JavaScript with a safety net and a much better IDE experience
TypeScript adds a powerful static type system to JavaScript, catching errors at compile time and making large codebases dramatically easier to maintain and refactor. This category covers type primitives, generics, utility types, declaration files, strict mode, and the patterns that make TypeScript an upgrade rather than just added ceremony.
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Covariance & Contravariance 4.7 Variance describes how subtype relationships on a type's components affect subtype relationships on the whole type — covariant types follow the direction, contravariant types reverse it.
4w ago
typescript advanced
Discriminated Unions 2.0 A union of types that each carry a shared literal field (the discriminant) allowing TypeScript to narrow exhaustively — the canonical way to model mutually exclusive states.
4w ago
typescript intermediate
Module Augmentation & Declaration Merging 2.0 Module augmentation lets you extend third-party or global type definitions without modifying their source — adding properties to existing interfaces, modules, or the global scope.
4w ago
typescript advanced
Recursive Types 3.7 Types that reference themselves to describe arbitrarily nested structures — trees, nested menus, JSON, linked lists — without requiring any escape hatch.
4w ago
typescript advanced
Type Guards & Narrowing 2.0 Type guards are expressions that narrow a union type to a more specific type at runtime — telling TypeScript exactly which branch of a union you're in.
4w ago
typescript intermediate
Branded / Opaque Types in TypeScript
A technique to make structurally identical types incompatible — a UserId and an OrderId are both strings, but branding makes them distinct types so passing an OrderId where UserId is expected is a compile-time error.
2mo ago
typescript advanced
const Type Parameters (TS 5.0) 5.0
TypeScript 5.0 const type parameters infer literal types instead of widened types — const T extends string[] infers ['a','b'] not string[].
2mo ago
typescript intermediate
Exhaustive Checks with never
Using the 'never' type in a default branch to make TypeScript error at compile time if a union type is not fully handled — ensures every new variant of a type forces a matching handler to be written.
2mo ago
typescript intermediate
infer Keyword in Conditional Types 2.8
The infer keyword inside conditional types lets TypeScript extract and name a type from within a generic structure — enabling ReturnType<T>, Awaited<T>, and custom type extraction.
2mo ago
typescript advanced
TypeScript Function Overloads
TypeScript function overloads allow a single function to accept different argument shapes and return different types based on which overload signature matches — providing precise type checking that union types alone cannot express.
2mo ago
typescript intermediate
using & await using (TS 5.2 Explicit Resource Management) 5.2
TypeScript 5.2 using keyword automatically disposes resources (DB connections, file handles) when they go out of scope — like C# using or Python with.
2mo ago
typescript advanced
satisfies Operator (TS 4.9) 4.9
satisfies validates that a value matches a type without widening the inferred type — keeping precise literal types while checking against an interface.
2mo ago
typescript intermediate
Template Literal Types 4.1
TypeScript template literal types combine string literals with type interpolation — type EventName = `on${Capitalize<string>}` — enabling precise string-pattern type constraints.
2mo ago
typescript advanced
Conditional Types & infer 2.8
Types that choose between two types based on a condition — T extends U ? X : Y — enabling type-level branching. The infer keyword extracts types from within a conditional.
2mo ago
typescript advanced
Mapped Types & Template Literal Types 2.1
Mapped types transform existing types by iterating over their keys. Template literal types create string union types from combinations — together they enable powerful type-level transformations.
2mo ago
typescript advanced
TypeScript Declaration Files (.d.ts) 2.0
Type-only files describing JavaScript code shapes — DefinitelyTyped (@types/* packages) provides community-maintained declarations for popular JS libraries.
2mo ago
typescript advanced
TypeScript Decorators 4.0
Metadata annotations on classes, methods, and properties — used in NestJS, Angular, TypeORM, and class-validator to attach behaviour declaratively.
2mo ago
typescript advanced
TypeScript Enums vs Const Enums vs Union Types 2.0
Three ways to define a set of named constants in TypeScript — regular enums emit JavaScript, const enums are inlined at compile time, and union types are the idiomatic zero-cost alternative.
2mo ago
typescript intermediate
TypeScript Modules & Namespaces 2.0
ES modules (import/export) are the modern standard — namespaces are legacy for global scripts and ambient declarations only.
2mo ago
typescript intermediate
TypeScript vs PHP Type System 4.0
TypeScript uses structural typing (shape compatibility); PHP uses nominal typing (explicit implements). TypeScript infers types; PHP requires annotations. Both support generics (PHP via PHPDoc).
2mo ago
typescript intermediate