From 04f5554ff598053f896ebaf27304f09e5f156bc8 Mon Sep 17 00:00:00 2001
From: Rico Kahler <rakahler@umich.edu>
Date: Sun, 3 Jan 2021 19:14:47 -0500
Subject: [PATCH] feat: is server side context type guard (#19)

* feat: is server side context type guard

* update readme

* Update README.md
---
 README.md                                | 27 +++++++++++++++++++++++-
 package-lock.json                        |  2 +-
 package.json                             |  2 +-
 src/index.ts                             |  1 +
 src/is-server-side-props-context.test.ts |  6 ++++++
 src/is-server-side-props-context.ts      | 14 ++++++++++++
 6 files changed, 49 insertions(+), 3 deletions(-)
 create mode 100644 src/is-server-side-props-context.test.ts
 create mode 100644 src/is-server-side-props-context.ts

diff --git a/README.md b/README.md
index a0cc440f..f255494b 100644
--- a/README.md
+++ b/README.md
@@ -103,6 +103,31 @@ const useBlogPost = createDataHook('BlogPost', async (context) => {
 export default useBlogPost;
 ```
 
+<details>
+<summary>
+TypeScript User?
+
+> Note: For TypeScript users, if you're planning on only using the data hook in the context of `getServerSideProps`, you can import the provided [type guard](https://www.typescriptlang.org/docs/handbook/advanced-types.html#user-defined-type-guards), `isServerSidePropsContext`, to narrow the type of the incoming context.
+
+</summary>
+
+```tsx
+import { createDataHook, isServerSidePropsContext } from 'next-data-hooks';
+
+const useServerSideData = createDataHook('Data', async (context) => {
+  if (!isServerSidePropsContext(context)) {
+    throw new Error('This data hook only works in getServerSideProps.');
+  }
+
+  // here, the type of `context` has been narrowed to the server side conext
+  const query = context.req.query;
+});
+
+export default useServerSideData;
+```
+
+</details>
+
 2. Use the data hook in a component. Add it to a static prop in an array with other data hooks to compose them downward.
 
 ```tsx
@@ -135,7 +160,7 @@ BlogPostComponent.dataHooks = [
 export default BlogPostComponent;
 ```
 
-3. Pass the data hooks down in `getStaticProps`.
+3. Pass the data hooks down in `getStaticProps` or `getServerSideProps`.
 
 ```tsx
 import { getDataHooksProps } from 'next-data-hooks';
diff --git a/package-lock.json b/package-lock.json
index 9e6bacac..ff8bfc35 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "next-data-hooks",
-  "version": "0.4.0",
+  "version": "0.5.0",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
diff --git a/package.json b/package.json
index 07bffb17..cc9f3649 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "next-data-hooks",
-  "version": "0.4.0",
+  "version": "0.5.0",
   "description": "Use `getStaticProps` as react hooks",
   "private": true,
   "scripts": {
diff --git a/src/index.ts b/src/index.ts
index 8b7b9ea0..fef97a2b 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -2,3 +2,4 @@ export { default as createDataHook } from './create-data-hook';
 export { default as getDataHooksProps } from './get-data-hooks-props';
 export { default as NextDataHooksContext } from './next-data-hooks-context';
 export { default as NextDataHooksProvider } from './next-data-hooks-provider';
+export { default as isServerSidePropsContext } from './is-server-side-props-context';
diff --git a/src/is-server-side-props-context.test.ts b/src/is-server-side-props-context.test.ts
new file mode 100644
index 00000000..88364457
--- /dev/null
+++ b/src/is-server-side-props-context.test.ts
@@ -0,0 +1,6 @@
+import isServerSidePropsContext from './is-server-side-props-context';
+
+it('returns true if there is a req and res', () => {
+  expect(isServerSidePropsContext({ req: true, res: true } as any)).toBe(true);
+  expect(isServerSidePropsContext({} as any)).toBe(false);
+});
diff --git a/src/is-server-side-props-context.ts b/src/is-server-side-props-context.ts
new file mode 100644
index 00000000..e89740a0
--- /dev/null
+++ b/src/is-server-side-props-context.ts
@@ -0,0 +1,14 @@
+import { GetServerSidePropsContext, GetStaticPropsContext } from 'next';
+
+function isServerSidePropsContext(
+  context: GetServerSidePropsContext | GetStaticPropsContext
+): context is GetServerSidePropsContext {
+  if (typeof context !== 'object' || !context) return false;
+
+  return (
+    !!(context as GetServerSidePropsContext).req &&
+    !!(context as GetServerSidePropsContext).res
+  );
+}
+
+export default isServerSidePropsContext;