Error map
IndexError IndexError: list index out of range
Python · layer 4, Application & API
Centre: this error. First ring: errors it is linked with (7). 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 (7)
ConnectionRefusedError: [Errno 111] Connection refused
Nothing is listening on the host/port Python tried to connect to.
java.lang.ArrayIndexOutOfBoundsException: Index 5 out of bounds for length 5
Code accessed an array index outside 0 … length-1.
java.lang.StringIndexOutOfBoundsException: begin 0, end 10, length 5
substring()/charAt() used an index outside the string.
Warning: Each child in a list should have a unique "key" prop
When rendering a list with `.map()`, each element needs a stable, unique `key` so React can track items between renders.
AttributeError: 'X' object has no attribute 'y'
You accessed an attribute or method that doesn’t exist on that object type.
Warning: `key` is not a prop. Trying to access it will result in `undefined` being returned.
A component tried to read props.key, which React reserves and never passes down.
RuntimeError: Event loop is closed
Async code tried to use an event loop that has already been shut down.
Two steps away (21)
Error: connect ECONNREFUSED 127.0.0.1:5432
Nothing is listening at that host:port — the target service is down or you’re connecting to the wrong address.
Cloudflare Error 521: Web Server Is Down
Cloudflare couldn’t connect to your origin — the connection was refused.
API Request Timed Out (ETIMEDOUT / ReadTimeout / timeout of 30000ms exceeded)
The client gave up waiting — either for the connection to open or for the response to arrive.
Warning: Undefined array key / Undefined index
Your code reads an array key that doesn’t exist — common with `$_GET`, `$_POST` and decoded JSON.
java.lang.UnsupportedOperationException (List.of / Arrays.asList is immutable)
Code tried to modify an immutable or fixed-size collection.
java.io.IOException: Stream closed
Code read or wrote a stream after it was closed — often by a try-with-resources block or a wrapper closing the underlying stream.
java.lang.ClassCastException: class A cannot be cast to class B
An object was cast to a type it isn’t.
java.lang.ArithmeticException: / by zero
Integer division or modulo by zero.
java.nio.file.AccessDeniedException: /path
The OS denied a file operation to the Java process.
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: 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: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined
JSX referenced a component that is undefined — almost always a default/named import mismatch.
TypeError: x is not a function
You called something as a function, but its value is not a function (it’s undefined, a string, an object…).
ImportError: cannot import name 'x' from 'y'
The module was found, but the name you’re importing from it doesn’t exist — usually a version change or a circular import.
KeyError: 'x'
You accessed a dictionary key that doesn’t exist.
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.
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.
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.
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).
AbortError: The user aborted a request. / signal is aborted without reason
A fetch was cancelled through an AbortController (or the browser cancelled it).
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