Error map

reduce empty TypeError: Reduce of empty array with no initial value

JavaScript · layer 1, On your device

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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.

1 · On your device 4 · Application & API
reduce empty — TypeError: Reduce of empty array with no initial value (JavaScript)reduce emptyUndefined array key — Warning: Undefined array key / Undefined index (PHP)Undefined array keyArrayIndexOutOfBoundsException — java.lang.ArrayIndexOutOfBoundsException: Index 5 out of bounds for length 5 (Java)ArrayIndexOutOfBoun…reading length — TypeError: Cannot read properties of undefined (reading 'length') (JavaScript)reading lengthAbortError — AbortError: The user aborted a request. / signal is aborted without reason (JavaScript)AbortErrorbody already used — TypeError: Failed to execute 'json' on 'Response': body stream already read (JavaScript)body already usedArray offset on null — Warning: Trying to access array offset on value of type null (PHP)Array offset on nullinvalid array length — RangeError: Invalid array length (JavaScript)invalid array lengthTypeError — TypeError: Cannot read properties of undefined (reading 'x') (JavaScript)TypeErrorHeaders already sent — Warning: Cannot modify header information - headers already sent (PHP)Headers already sentKeyError — KeyError: 'x' (Python)KeyErrorStringIndexOutOfBoundsException — java.lang.StringIndexOutOfBoundsException: begin 0, end 10, length 5 (Java)StringIndexOutOfBou…UnsupportedOperationException — java.lang.UnsupportedOperationException (List.of / Arrays.asList is immutable) (Java)UnsupportedOperatio…Stream closed — java.io.IOException: Stream closed (Java)Stream closedTypeError set undefined — TypeError: Cannot set properties of undefined (setting 'x') (JavaScript)TypeError set undef…addEventListener on null — TypeError: Cannot read properties of null (reading 'addEventListener') (JavaScript)addEventListener on…TypeError not iterable — TypeError: x is not iterable (JavaScript)TypeError not itera…Failed to fetch — TypeError: Failed to fetch / NetworkError when attempting to fetch resource (JavaScript)Failed to fetchUnhandledPromiseRejection — Node.js: [UnhandledPromiseRejection] — This error originated either by throwing inside of an async function without a catch block (Node.js)UnhandledPromiseRej…await outside async — SyntaxError: await is only valid in async functions and the top level bodies of modules (JavaScript)await outside asyncSocketException reset — java.net.SocketException: Connection reset (Java)SocketException res…URIError — URIError: URI malformed (JavaScript)URIErrorinvalid selector — DOMException: Failed to execute 'querySelector' on 'Document': 'x' is not a valid selector (JavaScript)invalid selectorObject.keys null — TypeError: Cannot convert undefined or null to object (JavaScript)Object.keys nullUndefined variable — Warning: Undefined variable $x (PHP)Undefined variableUndefined property — Warning: Undefined property: Class::$prop (PHP)Undefined propertyAw, Snap! — Chrome: Aw, Snap! Something went wrong while displaying this webpage. Error code: STATUS_ACCESS_VIOLATION / SIGILL / Out of Memory (Browser)Aw, Snap!

Directly related (7)

Undefined array keyPHP

Warning: Undefined array key / Undefined index

Your code reads an array key that doesn’t exist — common with `$_GET`, `$_POST` and decoded JSON.

ArrayIndexOutOfBoundsExceptionJava

java.lang.ArrayIndexOutOfBoundsException: Index 5 out of bounds for length 5

Code accessed an array index outside 0 … length-1.

reading lengthJavaScript

TypeError: Cannot read properties of undefined (reading 'length')

Code checked .length on something that is undefined — typically an array or string that hasn’t loaded.

AbortErrorJavaScript

AbortError: The user aborted a request. / signal is aborted without reason

A fetch was cancelled through an AbortController (or the browser cancelled it).

body already usedJavaScript

TypeError: Failed to execute 'json' on 'Response': body stream already read

A fetch Response body was consumed twice (e.g. calling .text() then .json()).

Array offset on nullPHP

Warning: Trying to access array offset on value of type null

Code used `$x['key']` where `$x` is null — usually a lookup or function that returned nothing.

invalid array lengthJavaScript

RangeError: Invalid array length

An array was created or resized with a negative, fractional or enormous length.

Two steps away (19)

TypeErrorJavaScript

TypeError: Cannot read properties of undefined (reading 'x')

You tried to access a property on a value that is `undefined` (or `null`) — usually data that hasn’t loaded yet or a wrong proper…

Headers already sentPHP

Warning: Cannot modify header information - headers already sent

You called `header()`, `setcookie()` or `session_start()` after output had already been sent to the browser.

KeyErrorPython

KeyError: 'x'

You accessed a dictionary key that doesn’t exist.

StringIndexOutOfBoundsExceptionJava

java.lang.StringIndexOutOfBoundsException: begin 0, end 10, length 5

substring()/charAt() used an index outside the string.

UnsupportedOperationExceptionJava

java.lang.UnsupportedOperationException (List.of / Arrays.asList is immutable)

Code tried to modify an immutable or fixed-size collection.

Stream closedJava

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.

TypeError set undefinedJavaScript

TypeError: Cannot set properties of undefined (setting 'x')

Code assigned a property on a value that is undefined (or null).

addEventListener on nullJavaScript

TypeError: Cannot read properties of null (reading 'addEventListener')

document.querySelector/getElementById returned null, so the element doesn’t exist when the script runs.

TypeError not iterableJavaScript

TypeError: x is not iterable

for…of, spread or destructuring was used on something that isn’t an array/iterable.

Failed to fetchJavaScript

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…

UnhandledPromiseRejectionNode.js

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.

await outside asyncJavaScript

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).

SocketException resetJava

java.net.SocketException: Connection reset

The remote side closed the TCP connection abruptly while Java was reading or writing.

URIErrorJavaScript

URIError: URI malformed

decodeURIComponent/decodeURI received an invalid percent-encoded sequence.

invalid selectorJavaScript

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.

Object.keys nullJavaScript

TypeError: Cannot convert undefined or null to object

Object.keys/entries/assign was called with undefined or null.

Undefined variablePHP

Warning: Undefined variable $x

PHP read a variable that was never assigned in the current scope.

Undefined propertyPHP

Warning: Undefined property: Class::$prop

Code read an object property that doesn’t exist on that object.

Aw, Snap!Browser

Chrome: Aw, Snap! Something went wrong while displaying this webpage. Error code: STATUS_ACCESS_VIOLATION / SIGILL / Out of Memory

A Chrome tab crashed — out of memory, a faulty extension, a graphics/driver issue or a very heavy page.

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