Error map
process.env.X is undefined in the browser (NEXT_PUBLIC_) Next.js: process.env.API_URL is undefined in Client Component / env variable not available in the browser
Next.js · layer 1, On your device
Centre: this error. First ring: errors it is linked with (10). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (10)
ReferenceError: React is not defined / 'React' must be in scope when using JSX
JSX was compiled with the classic runtime, which needs React imported in every file.
TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received undefined
A Node API got an argument of the wrong type — usually undefined because an env var or config value is missing.
npm update check failed — Try running with sudo or get access to the local update config store
npm’s update notifier couldn’t write its config — usually root-owned files in ~/.config from a past sudo npm.
Browser: Access to fetch at 'https://api.example.com/api/data' from origin 'https://app.example.com' has been blocked by CORS policy (Next.js route handler)
A cross-origin request to your Next.js API route is blocked because the response lacks CORS headers.
Next.js: You're importing a component that needs createContext. It only works in a Client Component but none of its parents are marked with "use client"
A context provider (or a lib that uses `createContext`) is used in a Server Component.
Next.js: ⨯ Conflicting app and page file was found, please remove the conflicting files to continue: "pages/index.tsx" - "app/page.tsx"
The same URL is defined in both the `app` and `pages` directories.
MongooseError: The `uri` parameter to `openUri()` must be a string, got "undefined". Make sure the first parameter to `mongoose.connect()` is a string
`mongoose.connect()` received `undefined` instead of a connection string — the environment variable wasn't loaded.
Next.js: FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory (during next build)
Node ran out of memory while building a large Next.js app (or on a small CI/Vercel runner).
Next.js: TypeError: Failed to parse URL from /api/posts (fetch in a Server Component)
`fetch('/api/x')` with a relative URL works in browsers but not on the server, which has no base URL.
Next.js: Error occurred prerendering page "/blog" TypeError: fetch failed { cause: Error: connect ECONNREFUSED 127.0.0.1:3000 }
During `next build` a page tried to fetch data from a server (often your own app or an API) that isn't running yet.
Two steps away (30)
ReferenceError: x is not defined
Code refers to a variable or function name that doesn’t exist in the current scope.
Error: Objects are not valid as a React child
You tried to render a plain object (or a Promise/Date) directly in JSX; React can only render strings, numbers, elements and arra…
Error: Nothing was returned from render. This usually means a return statement is missing.
A component returned undefined (React 17 and earlier) — usually a missing return or a return followed by a line break.
OAuth Error: redirect_uri_mismatch
The redirect URI in your OAuth request doesn’t exactly match one registered for the client in the provider’s console.
hint: You have divergent branches and need to specify how to reconcile them.
Git 2.27+ asks you to choose merge, rebase or fast-forward-only when local and remote both have new commits.
error: gpg failed to sign the data — fatal: failed to write commit object
Commit signing is enabled but GPG couldn’t sign — no TTY for the passphrase, wrong key, or agent not running.
npm ERR! code EACCES — permission denied
npm can’t write to a directory — usually global installs into a root-owned folder.
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?
The docker CLI can’t talk to the Docker engine — it isn’t running, or your user can’t access the socket.
OAuth 2.0 Error: invalid_scope / insufficient_scope
The requested scope is unknown or not allowed for this client — or the token lacks the scope the API endpoint requires.
Browser: Access to XMLHttpRequest at 'https://api.example.com' from origin 'http://localhost:3000' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header — Laravel
The browser blocked a cross-origin call to your Laravel API because the response lacks the right CORS headers.
Next.js: Warning: validateDOMNesting(...): <div> cannot appear as a descendant of <p> / In HTML, <p> cannot be a descendant of <p>. This will cause a hydration error
The rendered HTML has an invalid element nesting, so the browser "fixes" it and React's hydration no longer matches.
Next.js 15: Error: Route "/blog/[slug]" used `params.slug`. `params` should be awaited before using its properties
In Next.js 15 `params` and `searchParams` are Promises; reading properties synchronously triggers this error/warning.
Error: useNavigate() may be used only in the context of a <Router> component.
A React Router hook ran in a component that isn’t rendered inside a Router provider.
TypeError: Cannot destructure property 'user' of 'useContext(...)' as it is undefined.
A component read a context with no matching Provider above it.
Error: No QueryClient set, use QueryClientProvider to set one
TanStack Query hooks ran outside a QueryClientProvider (or a duplicate copy of the library is installed).
TypeError: Missing parameter name at 1 (path-to-regexp)
An Express 5 (path-to-regexp v8) route uses old wildcard syntax like '*' or '/:id?'.
No routes matched location "/x"
React Router found no route definition for the current URL.
Error occurred prerendering page "/x". Read more: https://nextjs.org/docs/messages/prerender-error
A page threw an error while Next.js was rendering it at build time.
MongooseError: Operation `users.find()` buffering timed out after 10000ms
Mongoose queued a query waiting for a connection that never opened.
MongoDB: MongoParseError: Invalid scheme, expected connection string to start with "mongodb://" or "mongodb+srv://"
The connection string is missing, malformed, or the environment variable holding it is undefined.
Mongoose: OverwriteModelError: Cannot overwrite `User` model once compiled.
`mongoose.model('User', schema)` was called twice with the same name, typically from hot reloading.
npm ERR! code ELIFECYCLE / Command failed with exit code 1
An npm script (build, start, test, postinstall) exited with an error. ELIFECYCLE is only the wrapper — the real error is printed…
gyp ERR! build error / node-gyp rebuild failed
A dependency with native C/C++ code couldn’t compile — missing build tools, Python, or an unsupported Node version.
FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory
The V8 heap hit its limit — a large build (webpack, tsc, Next.js) needs more memory, or the app leaks.
Error: Hydration failed because the initial UI does not match what was rendered on the server
The HTML rendered on the server differs from the first client render, so React (Next.js/Remix) can’t attach to it.
Warning: validateDOMNesting(...): <div> cannot appear as a descendant of <p>.
The JSX produces invalid HTML nesting, which also causes hydration mismatches in SSR.
Error: Dynamic server usage: Route /x couldn't be rendered statically because it used `cookies`
Next.js tried to statically render a route that reads request-specific data (cookies, headers, searchParams).
Error: error:0308010C:digital envelope routines::unsupported
An old build tool (webpack 4, old react-scripts) uses a hash algorithm that OpenSSL 3 in Node 17+ disables.
Error: @prisma/client did not initialize yet. Please run "prisma generate"
The generated Prisma Client is missing or out of date.
Error: Node Sass does not yet support your current environment
node-sass (deprecated) has no binary for your Node version/OS.
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