typescriptANYtypescriptgenericsfunctions
typescript
function identity<T>(value: T): T {
return value;
}Generics let a function preserve type information across inputs and outputs.
TypeScript Types and Generics
Advanced type operators, mapped types, conditional types, and utility types.
Export
Copy the compact sheet, download it, or print it.
Download
`D` dense toggle · `C` copy all
Generics
Reusable type parameters for functions, interfaces, and classes.
typescriptANYtypescriptgenericsarrays
typescript
function first<T>(items: T[]): T | undefined {
return items[0];
}A generic function can infer `T` from the array argument.
typescriptANYtypescriptgenericsinterface
typescript
interface ApiResponse<T> {
data: T;
error?: string;
}Generic interfaces are ideal for API wrappers and paginated result types.
typescriptANYtypescriptgenericsconstraints
typescript
function printLength<T extends { length: number }>(value: T) {
console.log(value.length);
}Constraints allow generic code to safely access known members.
typescriptANYtypescriptgenericskeyofindexed-access
typescript
function getProp<T, K extends keyof T>(obj: T, key: K): T[K] {
return obj[key];
}This is one of the most useful generic patterns in application code.
Type Operators
`keyof`, `typeof`, indexed access, and type queries.
typescriptANYtypescriptkeyof
typescript
type User = { id: number; name: string };
type UserKeys = keyof User; // "id" | "name"`keyof` is foundational for many advanced type helpers.
typescriptANYtypescripttypeof
typescript
const config = {
retries: 3,
cache: true,
};
type Config = typeof config;`typeof` in a type position is useful when a runtime object already defines the shape.
typescriptANYtypescriptindexed-access
typescript
type User = { profile: { email: string } };
type Email = User["profile"]["email"];Indexed access types help avoid repeating nested object types manually.
typescriptANYtypescripttemplate-literal-types
typescript
type Method = "GET" | "POST";
type Route = "/users" | "/posts";
type Endpoint = `${Method} ${Route}`;Template literal types are powerful for modeling event names, API routes, and CSS tokens.
Mapped and Conditional Types
Transform one type into another with reusable helpers.
typescriptANYtypescriptmapped-types
typescript
type Flags<T> = {
[K in keyof T]: boolean;
};Mapped types let you derive new object types from existing ones.
typescriptANYtypescriptconditional-types
typescript
type IsString<T> = T extends string ? true : false;Conditional types are the basis for many advanced utility helpers.
typescriptANYtypescriptconditional-typesinfer
typescript
type GetReturn<T> = T extends (...args: never[]) => infer R ? R : never;`infer` captures a type from a matched pattern in a conditional type.
typescriptANYtypescriptdiscriminated-unions
typescript
type Success = { kind: "success"; data: string };
type Failure = { kind: "error"; message: string };
type Result = Success | Failure;Discriminated unions pair especially well with narrowing in control flow.
Utility Types
Built-in helpers like Partial, Pick, Record, and Awaited.
typescriptANYtypescriptutility-typespartial
typescript
type User = { id: number; name: string; email: string };
type UserPatch = Partial<User>;Useful for patch/update payloads and intermediate object construction.
typescriptANYtypescriptutility-typesrequired
typescript
type User = { id?: number; name?: string };
type CompleteUser = Required<User>;Useful when optional data must be normalized before use.
typescriptANYtypescriptutility-typespick
typescript
type User = { id: number; name: string; email: string };
type PublicUser = Pick<User, "id" | "name">;Useful for API DTOs and lightweight derived shapes.
typescriptANYtypescriptutility-typesomit
typescript
type User = { id: number; passwordHash: string; email: string };
type SafeUser = Omit<User, "passwordHash">;A common pattern for removing internal or sensitive fields.
typescriptANYtypescriptutility-typesrecord
typescript
type FeatureFlag = "billing" | "search";
const flags: Record<FeatureFlag, boolean> = {
billing: true,
search: false,
};`Record` is often cleaner than a custom index signature.
typescriptANYtypescriptutility-typesawaited
typescript
type Result = Awaited<Promise<Promise<string>>>; // string`Awaited` models how `await` recursively unwraps promises.
typescriptANYtypescriptutility-typesreturntype
typescript
function createUser() {
return { id: 1, name: "Ada" };
}
type User = ReturnType<typeof createUser>;Useful when you want a type that stays synced with a function implementation.
More in TypeScript
TypeScript Utility Types and Recipes
Built-in utility types and practical application patterns.
TypeScript tsconfig and Tooling
tsconfig.json patterns, diagnostics, and project references.
TypeScript Classes and Modules
Classes, access modifiers, inheritance, modules, and validation boundaries.
TypeScript Functions and Narrowing
Function typing, overloads, control-flow narrowing, and async typing.
TypeScript Cheat Sheet
Core TypeScript syntax, typing patterns, and compiler commands.