Error map
async useEffect Warning: useEffect must not return anything besides a function, which is used for clean-up. It looks like you wrote useEffect(async () => ...)
React · layer 1, On your device
Centre: this error. First ring: errors it is linked with (9). 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 (9)
Warning: An update to Component inside a test was not wrapped in act(...)
A component updated state after the test’s synchronous assertions — async work wasn’t awaited.
Error: Invalid hook call. Hooks can only be called inside of the body of a function component.
A hook ran outside a function component/custom hook, conditionally — or two copies of React are loaded.
AbortError: The user aborted a request. / signal is aborted without reason
A fetch was cancelled through an AbortController (or the browser cancelled it).
TypeError: Failed to execute 'json' on 'Response': body stream already read
A fetch Response body was consumed twice (e.g. calling .text() then .json()).
RuntimeWarning: coroutine 'fetch' was never awaited
An async function was called without await, so it never ran.
Error: Maximum update depth exceeded. This can happen when a component repeatedly calls setState inside componentWillUpdate or componentDidUpdate.
A component keeps updating itself in an effect or lifecycle — usually a useEffect that sets state its own dependencies change.
Warning: useLayoutEffect does nothing on the server
A component using useLayoutEffect was server-rendered, where layout effects can’t run.
RuntimeError: Event loop is closed
Async code tried to use an event loop that has already been shut down.
React Hook useEffect has a missing dependency (react-hooks/exhaustive-deps)
ESLint warns that the effect reads a value that isn’t in its dependency array, so it may use a stale value.
Two steps away (22)
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.
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).
Warning: validateDOMNesting(...): <div> cannot appear as a descendant of <p>.
The JSX produces invalid HTML nesting, which also causes hydration mismatches in SSR.
npm ERR! code ERESOLVE — unable to resolve dependency tree
npm 7+ found conflicting peer dependency requirements and refuses to install a broken tree.
Error: Too many re-renders. React limits the number of renders to prevent an infinite loop.
A state update runs during render, which triggers another render, which updates state again — forever.
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.
TypeError: Failed to fetch / NetworkError when attempting to fetch resource
The browser couldn’t complete the request at the network level — CORS, DNS, offline, blocked mixed content, or the server refused…
TypeError: Reduce of empty array with no initial value
Array.reduce() ran on an empty array without an initial value.
RangeError: Invalid array length
An array was created or resized with a negative, fractional or enormous length.
java.net.SocketException: Connection reset
The remote side closed the TCP connection abruptly while Java was reading or writing.
URIError: URI malformed
decodeURIComponent/decodeURI received an invalid percent-encoded sequence.
DOMException: Failed to execute 'querySelector' on 'Document': 'x' is not a valid selector
The CSS selector string is invalid — often an ID starting with a digit or containing special characters.
error: externally-managed-environment
Your system Python (Debian 12+, Ubuntu 23.04+, Homebrew) refuses pip installs into the OS-managed environment (PEP 668).
Python was not found; run without arguments to install from the Microsoft Store
Windows ran the Microsoft Store “App execution alias” instead of a real Python installation.
RuntimeError: Working outside of application context.
Code used current_app, g, or a Flask extension (like SQLAlchemy) without an active Flask application context.
Warning: A component is changing an uncontrolled input to be controlled
An input’s `value` started as `undefined` (uncontrolled) and later became a defined value (controlled), or vice versa.
Warning: Cannot update a component (`Parent`) while rendering a different component (`Child`)
A child component updated a parent’s state during its render instead of in an effect or event handler.
Error: Actions must be plain objects. Instead, the actual type was: 'function'.
A function (thunk) was dispatched but the thunk middleware isn’t configured.
Warning: Prop `className` did not match. Server: "x" Client: "y"
A prop rendered on the server differs from the client — usually CSS-in-JS class names or random IDs.
TypeError: f() takes 1 positional argument but 2 were given
A function was called with more positional arguments than it accepts — very often a method missing `self`.
TypeError: f() missing 1 required positional argument: 'x'
A function was called without a required parameter.
IndexError: list index out of range
Code accessed a list position that doesn’t exist.
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