freeze build timestamp via an environment variable

.node-version

@@ -1 +1 @@
-16.14.1
+16.14.2

lib/config/constants.ts

@@ -1,2 +1,5 @@
 // Next.js constants (not needed in frontend)
 export const NOTES_DIR = "./notes";
+
+// normalize the timestamp saved when building/deploying (see next.config.js) and fall back to right now:
+export const RELEASE_DATE = new Date(process.env.RELEASE_DATE ?? Date.now()).toISOString();

lib/helpers/build-feed.ts

@@ -1,6 +1,7 @@
 import { Feed } from "feed";
 import { getAllNotes } from "./parse-notes";
 import * as config from "../config";
+import { RELEASE_DATE } from "../config/constants";
 import type { GetServerSidePropsContext, PreviewData } from "next";
 import type { ParsedUrlQuery } from "querystring";
 
@@ -20,7 +21,7 @@ export const buildFeed = (
     title: config.siteName,
     description: config.longDescription,
     copyright: "https://creativecommons.org/licenses/by/4.0/",
-    updated: new Date(),
+    updated: new Date(RELEASE_DATE),
     image: `${config.baseUrl}/static/images/me.jpg`,
     feedLinks: {
       rss: `${config.baseUrl}/feed.xml`,

next.config.js

@@ -23,6 +23,9 @@ module.exports = (phase, { defaultConfig }) => {
     trailingSlash: true,
     productionBrowserSourceMaps: true,
     env: {
+      // freeze build timestamp for when serverless pages need a "last updated" date:
+      RELEASE_DATE: new Date().toISOString(),
+      // check if we're running locally via `next dev`:
       IS_DEV_SERVER: phase === PHASE_DEVELOPMENT_SERVER,
     },
     images: {

package.json

@@ -107,7 +107,7 @@
   },
   "packageManager": "yarn@1.22.17",
   "volta": {
-    "node": "16.14.1",
+    "node": "16.14.2",
     "yarn": "1.22.17"
   }
 }

pages/sitemap.xml.ts

@@ -1,14 +1,21 @@
 import { getServerSideSitemap } from "next-sitemap";
 import { getAllNotes } from "../lib/helpers/parse-notes";
 import { baseUrl } from "../lib/config";
+import { RELEASE_DATE } from "../lib/config/constants";
 import type { GetServerSideProps } from "next";
 import type { ISitemapField } from "next-sitemap";
 
 export const getServerSideProps: GetServerSideProps = async (context) => {
   // TODO: make this not manual (serverless functions can't see filesystem at runtime)
   const pages: ISitemapField[] = [
-    { loc: "/", priority: 1.0, changefreq: "weekly" }, // homepage
+    {
-    { loc: "/notes/", changefreq: "weekly" },
+      // homepage
+      loc: "/",
+      priority: 1.0,
+      changefreq: "weekly",
+      lastmod: RELEASE_DATE,
+    },
+    { loc: "/notes/", changefreq: "weekly", lastmod: RELEASE_DATE },
     { loc: "/birthday/" },
     { loc: "/cli/" },
     { loc: "/contact/" },
@@ -28,7 +35,7 @@ export const getServerSideProps: GetServerSideProps = async (context) => {
     pages.push({
       loc: `/notes/${note.slug}/`,
       // pull lastMod from front matter date
-      lastmod: note.date,
+      lastmod: new Date(note.date).toISOString(),
       priority: 0.7,
     })
   );