Make it possible to type context and props for LoadInput and LoadOutp…

…ut (#1447) - added generics for Context, Page Params and Props - added a helper type "MaybePromise" to not write T | Promise<T> all the time - Make LoadInput/Output public Fixes #1442
sveltejs · May 31, 2021 · 1bf1a02 · 1bf1a02
1 parent 6b186ae
commit 1bf1a02
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Showing 6 changed files with 67 additions and 20 deletions.
diff --git a/.changeset/tricky-rockets-agree.md b/.changeset/tricky-rockets-agree.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Make it possible to type context, page params and props for LoadInput and LoadOutput
diff --git a/packages/kit/types/endpoint.d.ts b/packages/kit/types/endpoint.d.ts
@@ -1,5 +1,5 @@
 import { ServerRequest } from './hooks';
-import { Headers } from './helper';
+import { Headers, MaybePromise } from './helper';
 
 type JSONValue =
 	| string
@@ -18,4 +18,4 @@ export type EndpointOutput = {
 
 export type RequestHandler<Locals = Record<string, any>, Body = unknown> = (
 	request: ServerRequest<Locals, Body>
-) => void | EndpointOutput | Promise<EndpointOutput>;
+) => void | MaybePromise<EndpointOutput>;
diff --git a/packages/kit/types/helper.d.ts b/packages/kit/types/helper.d.ts
@@ -18,9 +18,14 @@ export type ParameterizedBody<Body = unknown> = Body extends FormData
 // but this can't happen until TypeScript 4.3
 export type Headers = Record<string, string>;
 
-export type Location = {
+export type Location<Params extends Record<string, string> = Record<string, string>> = {
 	host: string;
 	path: string;
-	params: Record<string, string>;
+	params: Params;
 	query: URLSearchParams;
 };
+
+export type MaybePromise<T> = T | Promise<T>;
+export type InferValue<T, Key extends keyof T, Default> = T extends Record<Key, infer Val>
+	? Val
+	: Default;
diff --git a/packages/kit/types/hooks.d.ts b/packages/kit/types/hooks.d.ts
@@ -1,4 +1,4 @@
-import { Headers, Location, ParameterizedBody } from './helper';
+import { Headers, Location, MaybePromise, ParameterizedBody } from './helper';
 
 export type StrictBody = string | Uint8Array;
 
@@ -24,10 +24,10 @@ export type ServerResponse = {
 };
 
 export type GetSession<Locals = Record<string, any>, Session = any> = {
-	(request: ServerRequest<Locals>): Session | Promise<Session>;
+	(request: ServerRequest<Locals>): MaybePromise<Session>;
 };
 
 export type Handle<Locals = Record<string, any>> = (input: {
 	request: ServerRequest<Locals>;
-	resolve: (request: ServerRequest<Locals>) => ServerResponse | Promise<ServerResponse>;
-}) => ServerResponse | Promise<ServerResponse>;
+	resolve: (request: ServerRequest<Locals>) => MaybePromise<ServerResponse>;
+}) => MaybePromise<ServerResponse>;
diff --git a/packages/kit/types/index.d.ts b/packages/kit/types/index.d.ts
@@ -5,7 +5,7 @@ import './ambient-modules';
 
 export { Adapter, AdapterUtils, Config, ValidatedConfig } from './config';
 export { EndpointOutput, RequestHandler } from './endpoint';
-export { ErrorLoad, Load, Page } from './page';
+export { ErrorLoad, Load, Page, LoadInput, LoadOutput, ErrorLoadInput } from './page';
 export {
 	Incoming,
 	GetSession,

diff --git a/packages/kit/types/page.d.ts b/packages/kit/types/page.d.ts
@@ -1,27 +1,64 @@
-import { Location as Page } from './helper';
+import { Location as Page, MaybePromise, InferValue } from './helper';
 
-export type LoadInput = {
-	page: Page;
+export type LoadInput<
+	PageParams extends Record<string, string> = Record<string, string>,
+	Context extends Record<string, any> = Record<string, any>
+> = {
+	page: Page<PageParams>;
 	fetch: (info: RequestInfo, init?: RequestInit) => Promise<Response>;
 	session: any;
-	context: Record<string, any>;
+	context: Context;
 };
 
-export type ErrorLoadInput = LoadInput & {
+export type ErrorLoadInput<
+	PageParams extends Record<string, string> = Record<string, string>,
+	Context extends Record<string, any> = Record<string, any>
+> = LoadInput<PageParams, Context> & {
 	status: number;
 	error: Error;
 };
 
-export type LoadOutput = {
+export type LoadOutput<
+	Props extends Record<string, any> = Record<string, any>,
+	Context extends Record<string, any> = Record<string, any>
+> = {
 	status?: number;
 	error?: string | Error;
 	redirect?: string;
-	props?: Record<string, any> | Promise<Record<string, any>>;
-	context?: Record<string, any>;
+	props?: Props;
+	context?: Context;
 	maxage?: number;
 };
 
-/* Publicized Types */
-export type Load = (input: LoadInput) => LoadOutput | Promise<LoadOutput>;
-export type ErrorLoad = (input: ErrorLoadInput) => LoadOutput | Promise<LoadOutput>;
+// Publicized Types
+export type Load<
+	Input extends { context?: Record<string, any>; pageParams?: Record<string, string> } = {},
+	Output extends { context?: Record<string, any>; props?: Record<string, any> } = {}
+> = (
+	input: LoadInput<
+		InferValue<Input, 'pageParams', Record<string, string>>,
+		InferValue<Input, 'context', Record<string, any>>
+	>
+) => MaybePromise<
+	LoadOutput<
+		InferValue<Output, 'props', Record<string, any>>,
+		InferValue<Output, 'context', Record<string, any>>
+	>
+>;
+
+export type ErrorLoad<
+	Input extends { context?: Record<string, any>; pageParams?: Record<string, string> } = {},
+	Output extends { context?: Record<string, any>; props?: Record<string, any> } = {}
+> = (
+	input: ErrorLoadInput<
+		InferValue<Input, 'pageParams', Record<string, string>>,
+		InferValue<Input, 'context', Record<string, any>>
+	>
+) => MaybePromise<
+	LoadOutput<
+		InferValue<Output, 'props', Record<string, any>>,
+		InferValue<Output, 'context', Record<string, any>>
+	>
+>;
+
 export { Page };