Christopher Tran pfftdammitchris

💭

Dreaming

JavaScript Developer. React, NodeJS, TypeScript

pfftdammitchris / snippet-11.ts

Created July 18, 2026 06:06

TypeScript Generic Constraints in Depth: `extends`, `keyof`, and the Patterns That Prevent Runtime Errors - snippet-11.ts

	interface DatabaseConfig {
	host: string;
	port: number;
	ssl: boolean;
	poolSize: number;
	}

	const defaults: Partial<DatabaseConfig> = {
	ssl: true,
	poolSize: 10,

pfftdammitchris / snippet-12.ts

Created July 18, 2026 06:06

TypeScript Generic Constraints in Depth: `extends`, `keyof`, and the Patterns That Prevent Runtime Errors - snippet-12.ts

	type RequiredFields = "url" \| "method";

	class RequestBuilder<T extends Partial<Record<RequiredFields, unknown>>> {
	private data: T = {} as T;

	url<U extends string>(value: U): RequestBuilder<T & { url: U }> {
	this.data.url = value as any;
	return this as any;
	}

pfftdammitchris / snippet-13.ts

Created July 18, 2026 06:06

TypeScript Generic Constraints in Depth: `extends`, `keyof`, and the Patterns That Prevent Runtime Errors - snippet-13.ts

	interface Endpoints {
	"/users": { id: number; name: string }[];
	"/users/:id": { id: number; name: string; email: string };
	"/posts": { id: number; title: string; authorId: number }[];
	}

	async function get<P extends keyof Endpoints>(path: P): Promise<Endpoints[P]> {
	const response = await fetch(`https://api.example.com${path}`);
	return response.json();
	}

pfftdammitchris / snippet-1.ts

Created July 18, 2026 05:06

TypeScript Variadic Tuple Types: Composing Function Signatures and Middleware Pipelines - snippet-1.ts

	// Basic variadic tuple type
	type Head<T extends any[]> = T extends [infer First, ...any[]] ? First : never;
	type Tail<T extends any[]> = T extends [any, ...infer Rest] ? Rest : never;

	// Usage
	type Numbers = [1, 2, 3, 4];
	type First = Head<Numbers>; // 1
	type Rest = Tail<Numbers>; // [2, 3, 4]

pfftdammitchris / snippet-2.ts

Created July 18, 2026 05:06

TypeScript Variadic Tuple Types: Composing Function Signatures and Middleware Pipelines - snippet-2.ts

	type Func<Args extends any[], Return> = (...args: Args) => Return;

	type Pipe<Fns extends Func<any, any>[]> =
	Fns extends [Func<infer A, infer B>, ...infer Rest]
	? Rest extends Func<any, any>[]
	? B extends Parameters<Rest[0]>[0]
	? Pipe<[Func<A, ReturnType<Rest[0]>>, ...Tail<Rest>]>
	: never
	: Func<A, B>
	: never;

pfftdammitchris / snippet-3.ts

Created July 18, 2026 05:06

TypeScript Variadic Tuple Types: Composing Function Signatures and Middleware Pipelines - snippet-3.ts

	type PipeFn = (arg: any) => any;

	type LastReturn<Fns extends PipeFn[]> =
	Fns extends [...any[], infer Last]
	? Last extends PipeFn
	? ReturnType<Last>
	: never
	: never;

	type ValidatePipe<Fns extends PipeFn[], Acc = []> =

pfftdammitchris / snippet-4.ts

Created July 18, 2026 05:06

TypeScript Variadic Tuple Types: Composing Function Signatures and Middleware Pipelines - snippet-4.ts

	type Middleware<In, Out> = (context: In) => Out \| Promise<Out>;

	type PipelineResult<
	Ctx,
	Middlewares extends Middleware<any, any>[]
	> = Middlewares extends [
	Middleware<infer In, infer Out>,
	...infer Rest
	]
	? Rest extends Middleware<any, any>[]

pfftdammitchris / snippet-5.ts

Created July 18, 2026 05:06

TypeScript Variadic Tuple Types: Composing Function Signatures and Middleware Pipelines - snippet-5.ts

	type Curry<P extends any[], R> =
	P extends [infer First, ...infer Rest]
	? (arg: First) => Rest extends []
	? R
	: Curry<Rest, R>
	: R;

	function curry<P extends any[], R>(
	fn: (...args: P) => R
	): Curry<P, R> {

pfftdammitchris / snippet-6.ts

Last active July 18, 2026 05:06

TypeScript Variadic Tuple Types: Composing Function Signatures and Middleware Pipelines - snippet-6.ts

	type ExpressRequest = { method: string; url: string };
	type ExpressResponse = { send: (data: any) => void };
	type NextFunction = () => void;

	type Middleware<Req, Res> = (
	req: Req,
	res: Res,
	next: NextFunction
	) => void \| Promise<void>;

pfftdammitchris / snippet-7.ts

Created July 18, 2026 05:06

TypeScript Variadic Tuple Types: Composing Function Signatures and Middleware Pipelines - snippet-7.ts