Error map
Unexpected token < SyntaxError: Unexpected token '<' (HTML served instead of JavaScript)
JavaScript · layer 1, On your device
Centre: this error. First ring: errors it is linked with (12). 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 (12)
Failed to load module script: Expected a JavaScript module script but the server responded with a MIME type of "text/html"
A or dynamic import got HTML back instead of JavaScript.
SyntaxError: Identifier 'x' has already been declared
The same let/const/class name was declared twice in the same scope.
SyntaxError: await is only valid in async functions and the top level bodies of modules
await was used inside a function that isn’t async (or in a classic, non-module script).
PHP still runs old code after deploy (OPcache not reset)
OPcache keeps serving cached bytecode, so changes uploaded to the server don’t take effect.
Dockerfile parse error line N: unknown instruction
A line in the Dockerfile doesn’t start with a valid instruction — usually a broken line continuation or a typo.
Refused to execute script from 'x' because its MIME type ('text/html') is not executable
The browser fetched a script but the server labelled it text/html (usually an error page), so it refused to run it.
SyntaxError: Invalid or unexpected token
The code contains a character the parser can’t handle — smart quotes, stray characters or an unterminated string.
SyntaxError: Invalid regular expression: /x/: Unterminated group
A regex pattern has invalid syntax — unbalanced parentheses/brackets or unescaped special characters.
SyntaxError: Unexpected token < in JSON at position 0
`JSON.parse()` / `response.json()` received something that isn’t JSON — very often an HTML error page.
SyntaxError: Unexpected identifier
The parser found a name where it expected punctuation — usually a missing comma, operator or quote.
The framework 'Microsoft.NETCore.App', version '8.0.0' (x64) was not found. You must install or update .NET to run this application
The machine doesn’t have the .NET runtime version the app was built for (framework-dependent deployment).
SyntaxError: missing ) after argument list
A function call’s parentheses are unbalanced — often an unescaped quote or a missing comma/plus.
Two steps away (30)
Azure App Service: ":( Application Error" / container didn’t respond to HTTP pings
App Service started your app but it crashed or never listened on the expected port.
Could not load file or assembly 'X, Version=…' or one of its dependencies
The runtime couldn’t find or load a referenced DLL — missing from the output, wrong version, or wrong platform (x86/x64).
ChunkLoadError: Loading chunk 123 failed.
A lazily loaded JavaScript chunk couldn’t be downloaded — usually because a new deployment removed the old hashed files.
ReferenceError: x is not defined
Code refers to a variable or function name that doesn’t exist in the current scope.
NameError: name 'x' is not defined
Python doesn’t know the name — it was never assigned/imported in this scope, or it’s misspelled.
SyntaxError: Unexpected end of input
The parser reached the end of the code (or JSON) while still expecting more — a missing } ) ] or empty JSON.
IndentationError: unexpected indent / expected an indented block
Python’s block structure is broken — inconsistent indentation or mixed tabs and spaces.
Node.js: [UnhandledPromiseRejection] — This error originated either by throwing inside of an async function without a catch block
A promise rejected and nothing handled it; since Node 15 this crashes the process.
AbortError: The user aborted a request. / signal is aborted without reason
A fetch was cancelled through an AbortController (or the browser cancelled it).
FastCGI sent in stderr: "Primary script unknown"
Nginx passed a script path to PHP-FPM that PHP-FPM couldn’t find — usually a wrong SCRIPT_FILENAME or root.
Nginx: [crit] connect() to unix:/run/php/php8.3-fpm.sock failed (13: Permission denied) while connecting to upstream
Nginx can't open the PHP-FPM (or app) Unix socket because of socket ownership/permissions or SELinux.
Nginx: [error] FastCGI sent in stderr: "PHP message: PHP Fatal error: Uncaught Error: Call to undefined function mysqli_connect()" while reading response header from upstream
PHP wrote an error to stderr while handling the request, so Nginx logs it (often a 500/502 follows).
PHP Parse error: syntax error, unexpected …
PHP can’t parse the file because of a syntax mistake — the real error is often on the line before the one reported.
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.
Console: Refused to apply style from 'https://…/style.css' because its MIME type ('text/html') is not a supported stylesheet MIME type
The stylesheet URL returned something that is not CSS — usually a 404/HTML error page — and `X-Content-Type-Options: nosniff` mak…
Console: Failed to register a ServiceWorker: A bad HTTP response code (404) was received when fetching the script
The browser could not fetch, parse or install the service worker script, or the page is not allowed to register one (HTTPS and sc…
DevTools: Failed to load source map — Could not load content for https://…/app.js.map: HTTP error: status code 404
DevTools could not download the `.map` file that a script or stylesheet points to, so you see minified code instead of your sourc…
SyntaxError: invalid syntax
Python couldn’t parse the code. The caret (^) points at or just after the mistake.
GraphQL: Syntax Error: Expected Name, found <EOF> / Unexpected }
The GraphQL document is malformed — unbalanced braces, a stray comma/character, or an empty query.
TypeScript: error TS1005: ';' expected.
The parser hit a syntax error — missing punctuation, mismatched brackets, or an unsupported syntax for your TypeScript version.
Adjacent JSX elements must be wrapped in an enclosing tag. Did you want a JSX fragment <>...</>?
A component returns two sibling JSX elements without a single parent.
TypeScript: error TS1128: Declaration or statement expected.
The parser found a token where a declaration or statement should start — usually stray braces/parentheses or code outside a funct…
Vue: [plugin:vite:vue] Element is missing end tag. / Invalid end tag.
The template has unbalanced HTML tags.
HTTP 400 Bad Request
The server could not understand the request because its syntax, headers or body are malformed or invalid.
HTTP 404 Not Found
The server can’t find anything at the requested URL.
HTTP 500 Internal Server Error
The server hit an unexpected condition — usually an unhandled exception or misconfiguration in the application.
HTTP Error 500.30 - ASP.NET Core app failed to start
IIS/Azure’s ASP.NET Core Module launched your app but it crashed during startup.
java.lang.UnsupportedClassVersionError: class file version 61.0, this version of the Java Runtime only recognizes up to 55.0
Code compiled for a newer Java version is running on an older JVM.
error NETSDK1045: The current .NET SDK does not support targeting .NET 8.0. Either target .NET 7.0 or lower, or use a version of the .NET SDK that supports .NET 8.0
The installed .NET SDK is older than the project’s TargetFramework.
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