From 1e4372c62763d92914dc1ef56f90c1329d035a82 Mon Sep 17 00:00:00 2001
From: JJ Kasper <22380829+ijjk@users.noreply.github.com>
Date: Wed, 13 Mar 2019 13:39:05 -0500
Subject: [PATCH] Show a better error when someone throws undefined (#6646)

* Show a better error when someone throws undefined

* Update error wording

Co-Authored-By: ijjk <22380829+ijjk@users.noreply.github.com>

* Update error wording in test

Co-Authored-By: ijjk <22380829+ijjk@users.noreply.github.com>

* Update test and add check for statusCode
before updating error
---
 package.json                                    |  3 ++-
 packages/next-server/server/next-server.ts      |  2 +-
 packages/next/server/next-dev-server.js         |  4 ++++
 test/integration/basic/pages/throw-undefined.js | 11 +++++++++++
 test/integration/basic/test/rendering.js        |  5 +++++
 5 files changed, 23 insertions(+), 2 deletions(-)
 create mode 100644 test/integration/basic/pages/throw-undefined.js

diff --git a/package.json b/package.json
index 7b6c6834a9..805863ea40 100644
--- a/package.json
+++ b/package.json
@@ -51,7 +51,8 @@
       "packages/next/build/webpack/plugins/terser-webpack-plugin/**",
       "examples/with-ioc/**",
       "examples/with-kea/**",
-      "examples/with-mobx/**"
+      "examples/with-mobx/**",
+      "test/integration/basic/pages/throw-undefined.js"
     ]
   },
   "devDependencies": {
diff --git a/packages/next-server/server/next-server.ts b/packages/next-server/server/next-server.ts
index 4c3c2496a3..01a2b272b6 100644
--- a/packages/next-server/server/next-server.ts
+++ b/packages/next-server/server/next-server.ts
@@ -307,7 +307,7 @@ export default class Server {
       )
       return html
     } catch (err) {
-      if (err.code === 'ENOENT') {
+      if (err && err.code === 'ENOENT') {
         res.statusCode = 404
         return this.renderErrorToHTML(null, req, res, pathname, query)
       } else {
diff --git a/packages/next/server/next-dev-server.js b/packages/next/server/next-dev-server.js
index 1ac2130d2e..bacb476b60 100644
--- a/packages/next/server/next-dev-server.js
+++ b/packages/next/server/next-dev-server.js
@@ -120,6 +120,10 @@ export default class DevServer extends Server {
       return super.renderErrorToHTML(compilationErr, req, res, pathname, query)
     }
 
+    if (!err && res.statusCode === 500) {
+      err = new Error('An undefined error was thrown sometime during render...')
+    }
+
     try {
       const out = await super.renderErrorToHTML(err, req, res, pathname, query)
       return out
diff --git a/test/integration/basic/pages/throw-undefined.js b/test/integration/basic/pages/throw-undefined.js
new file mode 100644
index 0000000000..6309859fb7
--- /dev/null
+++ b/test/integration/basic/pages/throw-undefined.js
@@ -0,0 +1,11 @@
+function ThrowUndefined (props) {
+  return (
+    <div>throw-undefined</div>
+  )
+}
+
+ThrowUndefined.getInitialProps = () => {
+  throw undefined
+}
+
+export default ThrowUndefined
\ No newline at end of file
diff --git a/test/integration/basic/test/rendering.js b/test/integration/basic/test/rendering.js
index 43cbf11878..65f9a9130b 100644
--- a/test/integration/basic/test/rendering.js
+++ b/test/integration/basic/test/rendering.js
@@ -289,5 +289,10 @@ export default function ({ app }, suiteName, render, fetch) {
         expect($('#asPath').text()).toBe('Current asPath: /nav/with-hoc')
       })
     })
+
+    it('should show a valid error when undefined is thrown', async () => {
+      const $ = await get$('/throw-undefined')
+      expect($('body').text()).toMatch('An undefined error was thrown sometime during render...')
+    })
   })
 }