From 52f75369efe5a0a1b320478984c90b6727d52159 Mon Sep 17 00:00:00 2001
From: Oleksii Tymoshenko <alextim@users.noreply.github.com>
Date: Mon, 27 Jun 2022 21:02:00 +0300
Subject: [PATCH] =?UTF-8?q?feat:=20better=20behavior=20for=20'undefined'?=
 =?UTF-8?q?=20return=20values=20from=20'serialize=E2=80=A6=20(#3723)?=
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* feat: better behavior with 'undefined' return values after 'serialize' func

* build: changeset added
---
 .changeset/tidy-dots-own.md                |  5 +++++
 packages/integrations/sitemap/README.md    |  7 ++++++-
 packages/integrations/sitemap/src/index.ts | 10 ++++++++--
 3 files changed, 19 insertions(+), 3 deletions(-)
 create mode 100644 .changeset/tidy-dots-own.md

diff --git a/.changeset/tidy-dots-own.md b/.changeset/tidy-dots-own.md
new file mode 100644
index 000000000..a9367dc2a
--- /dev/null
+++ b/.changeset/tidy-dots-own.md
@@ -0,0 +1,5 @@
+---
+'@astrojs/sitemap': patch
+---
+
+fix: if `serialize` function returns `undefined` for the passed entry, such entry will be excluded from sitemap
diff --git a/packages/integrations/sitemap/README.md b/packages/integrations/sitemap/README.md
index a2e7b73d9..e37a1ed86 100644
--- a/packages/integrations/sitemap/README.md
+++ b/packages/integrations/sitemap/README.md
@@ -222,7 +222,9 @@ The `LinkItem` type has two required fields: `url` (the fully-qualified URL for
 
 The `serialize` function should return `SitemapItem`, touched or not.  
 
-The example below shows the ability to add the sitemap specific properties individually.
+To exclude the passed entry from sitemap it should return `undefined`.
+
+The example below shows the ability to exclude certain entries and add the sitemap specific properties individually.
 
 __astro.config.mjs__
 
@@ -234,6 +236,9 @@ export default {
   integrations: [
     sitemap({
       serialize(item) {
+        if (/exclude-from-sitemap/.test(item.url)) {
+          return undefined;
+        }
         if (/your-special-page/.test(item.url)) {
           item.changefreq = 'daily';
           item.lastmod = new Date();
diff --git a/packages/integrations/sitemap/src/index.ts b/packages/integrations/sitemap/src/index.ts
index 2e1fa5a6e..67990b041 100644
--- a/packages/integrations/sitemap/src/index.ts
+++ b/packages/integrations/sitemap/src/index.ts
@@ -38,7 +38,7 @@ export type SitemapOptions =
 			priority?: number;
 
 			// called for each sitemap item just before to save them on disk, sync or async
-			serialize?(item: SitemapItem): SitemapItem | Promise<SitemapItem>;
+			serialize?(item: SitemapItem): SitemapItem | Promise<SitemapItem | undefined> | undefined;
 	  }
 	| undefined;
 
@@ -117,8 +117,14 @@ const createPlugin = (options?: SitemapOptions): AstroIntegration => {
 							const serializedUrls: SitemapItem[] = [];
 							for (const item of urlData) {
 								const serialized = await Promise.resolve(serialize(item));
-								serializedUrls.push(serialized);
+                if (serialized) {
+                  serializedUrls.push(serialized);
+                }
 							}
+              if (serializedUrls.length === 0) {
+                logger.warn('No pages found!');
+                return;
+              }							
 							urlData = serializedUrls;
 						} catch (err) {
 							logger.error(`Error serializing pages\n${(err as any).toString()}`);