Add warning for missing <Head> (vercel#8276)

devknoll · Timer · commit 04cf77970256 · 2019-08-11T22:48:05.000-04:00
* Add warning for missing &lt;Head&gt;

* Update the warning to be eliminated away in production

* Update head-manager.js
diff --git a/errors/next-head-count-missing.md b/errors/next-head-count-missing.md
@@ -0,0 +1,11 @@
+# `next-head-count` is missing
+
+#### Why This Error Occurred
+
+You have a custom `pages/_document.js` that doesn't have the components required for Next.js to render correctly.
+
+#### Possible Ways to Fix It
+
+Ensure that your `_document.js` is importing and rendering all of the [required components](https://nextjs.org/docs#custom-document).
+
+In this case you are most likely not rendering the `<Head>` component imported from `next/document`.
diff --git a/packages/next/client/head-manager.js b/packages/next/client/head-manager.js
@@ -47,6 +47,15 @@ export default class HeadManager {
   updateElements (type, components) {
     const headEl = document.getElementsByTagName('head')[0]
     const headCountEl = headEl.querySelector('meta[name=next-head-count]')
+    if (process.env.NODE_ENV !== 'production') {
+      if (!headCountEl) {
+        console.error(
+          'Warning: next-head-count is missing. https://err.sh/next.js/next-head-count-missing'
+        )
+        return
+      }
+    }
+
     const headCount = Number(headCountEl.content)
     const oldTags = []
 
