api: "YAML JSON TOON Database"
version: 1.0.0
format: json
dataset:
  id: 21
  slug: typescript-type-system
  title: "TypeScript Type System"
  description: "TypeScript's static type system: types, interfaces, generics, utility types, and advanced type manipulation."
  category: "Programming Languages"
  category_slug: programming-languages
  tags: "typescript,types,static-typing,generics,interfaces"
  view_count: 0
  created_at: 1777673262
  updated_at: 1777673262
data:
  concepts
    -
      name: "Primitive Types"
      types:
        [7]: string,number,boolean,null,undefined,symbol,bigint
      description: "Basic built-in types. TypeScript adds `any`, `unknown`, `never`, `void`."
      example: "let name: string = \"Alice\"; let age: number = 30; let isActive: boolean = true;"
    -
      name: Interfaces
      keyword: interface
      description: "Define object shape; can be extended and implemented. Structural typing."
      example: "interface User { id: number; name: string; email?: string; }
const u: User = { id: 1, name: \"Bob\" };"
    -
      name: "Type Aliases"
      keyword: type
      description: "Create new named type; can represent primitives, unions, tuples, objects."
      example: "type ID = number | string; type Point = [number, number]; type User = { name: string };"
    -
      name: Generics
      keyword: <T>
      description: "Type variables enable reusable components that work with multiple types."
      example: "function identity<T>(arg: T): T { return arg; }
let output = identity<string>(\"hello\");"
    -
      name: "Union Types"
      keyword: |
      description: "Value can be one of several types; use type guards to narrow."
      example: "function format(x: string | number) { if (typeof x === 'string') { ... } else { ... } }"
    -
      name: "Intersection Types"
      keyword: &
      description: "Combine multiple types into one; object must satisfy all constraints."
      example: "type Admin = User & { permissions: string[] };"
    -
      name: "Type Guards"
      patterns:
        [4]: typeof,instanceof,"in operator","custom type predicate"
      description: "Narrow types within conditional blocks."
      example: "function isString(x: unknown): x is string { return typeof x === 'string'; }
if (isString(val)) { val.toUpperCase(); }"
    -
      name: "Utility Types"
      common:
        [6]: Partial<T>,Required<T>,"Pick<T,K>","Omit<T,K>","Record<K,T>",ReturnType<T>
      description: "Built-in type transformations; avoid manual re-declaration."
      example: "interface Post { title: string; content: string; published: boolean; }
type EditPost = Pick<Post, 'title' | 'content'>;"
    -
      name: "Discriminated Unions"
      pattern: "tagged union"
      description: "Union of types with common literal field; enables exhaustive type checking in switch."
      example: "type Shape = { kind: 'circle'; radius: number } | { kind: 'square'; side: number };
function area(s: Shape) { switch(s.kind) { case 'circle': return Math.PI * s.radius ** 2; ... } }"
    -
      name: "Mapped Types"
      keyword: "keyof, in"
      description: "Create types by mapping over properties of another type."
      example: "type Readonly<T> = { readonly [P in keyof T]: T[P]; }
type Optional<T> = { [P in keyof T]?: T[P] };"
    -
      name: "Conditional Types"
      keyword: "T extends U ? X : Y"
      description: "Types that choose between two types based on a condition."
      example: "type IsString<T> = T extends string ? true : false;
type NonNullable<T> = T extends null | undefined ? never : T;"
    -
      name: "Template Literal Types"
      keyword: "`${}`"
      description: "Build strings from other types; useful for CSS property names, API endpoints."
      example: "type EventName = `on${Capitalize<string>}`; // onLoad, onMouseEnter, etc."