Error Message Decoder

Every error the decoder recognises

• Access to fetch has been blocked by CORS policy JavaScript
  The request often did reach the server; the browser just refused to let your script read the response. For security reasons the details are not available to JavaScript, so your catch only sees a generic network failure. Fix it →
• SyntaxError: Unexpected end of JSON input JavaScript
  JSON.parse or response.json() threw because the text isn't strict JSON. An empty string is not valid JSON. Fix it →
• SyntaxError: "[object Object]" is not valid JSON JavaScript
  JSON.parse or response.json() threw because the text isn't strict JSON. An object was converted to the string "[object Object]" and then parsed. Fix it →
• SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON JavaScript
  JSON.parse or response.json() threw because the text isn't strict JSON. The text starts with <, which means an HTML page (often an error page) was parsed as JSON. Fix it →
• SyntaxError: Expected double-quoted property name in JSON (and other JSON.parse errors) JavaScript
  JSON.parse or response.json() threw because the text isn't strict JSON. Firefox prefixes these messages with JSON.parse:. Fix it →
• TypeError: Cannot read properties of undefined (reading 'x') JavaScript
  You read a property, or called a method, on something that turned out to be undefined or null. The property name in the message is the one you were reading; the thing that was undefined is whatever sits to its left. Fix it →
• TypeError: undefined is not an object (Safari) JavaScript
  This is Safari's wording for reading a property of undefined or null. You read a property, or called a method, on something that turned out to be undefined or null. Fix it →
• TypeError: "x" is undefined (Firefox) JavaScript
  This is Firefox's wording for reading a property of undefined or null. You read a property, or called a method, on something that turned out to be undefined or null. Fix it →
• TypeError: x is not a function JavaScript
  You put () after something that isn't callable. All three engines use essentially the same wording. Fix it →
• TypeError: Assignment to constant variable JavaScript
  const makes the binding read-only, not the value. Changing obj.foo on a const obj is fine; writing obj = {} is not. Fix it →
• IndentationError / TabError Python
  In Python, indentation is syntax: the interpreter uses it to decide which lines belong to a block. TabError is a subclass of IndentationError, which is itself a SyntaxError. Fix it →
• SyntaxError: Missing parentheses in call to 'print' Python
  This is the classic Python 2 habit: print "hi" is a statement in Python 2 but a syntax error in Python 3. Fix it →
• SyntaxError (Python) Python
  The parser couldn't read the code. Since Python 3.10 the message usually explains itself, for example '(' was never closed or expected ':'. Fix it →
• NameError: name 'x' is not defined. Did you forget to import 'x'? Python
  A NameError is raised when a local or global name is not found. Here the name is a module you used without importing it. Fix it →
• NameError: name 'x' is not defined Python
  A NameError is raised when a local or global name is not found. Fix it →
• UnboundLocalError: cannot access local variable Python
  If a function assigns to a name anywhere in its body, Python treats that name as local for the whole function, so a read like count += 1 happens before any local value exists. Fix it →
• TypeError: 'NoneType' object is not subscriptable Python
  You indexed into None. NoneType errors usually trace back to a function that returned None. Fix it →
• TypeError: unsupported operand type(s) for +: 'int' and 'str' Python
  An operation was applied to an object of inappropriate type, here an operator used on two types that don't support it together. Fix it →
• TypeError: can only concatenate str (not "int") to str Python
  An operation was applied to an object of inappropriate type: you tried to join a str and a non-str with +. Fix it →
• TypeError: 'int' object is not callable Python
  You called something that isn't a function. Fix it →
• AttributeError: 'NoneType' object has no attribute 'x' Python
  The value is None, so it has none of the attributes you expected. This plays the role of JavaScript's Cannot read properties of undefined. Fix it →
• AttributeError: object has no attribute Python
  An attribute lookup or assignment failed. Either the method belongs to another type (Python lists use append, not JavaScript's push) or the value is None. Fix it →
• KeyError Python
  A dict key is missing. KeyError is a LookupError subclass. Fix it →
• IndexError: list index out of range Python
  A sequence index is out of range. IndexError is a LookupError subclass. Fix it →
• ValueError Python
  The argument had the right type but an unusable value. User input and file parsing are the usual sources. Fix it →
• ModuleNotFoundError: No module named 'x' Python
  The package isn't installed for the interpreter that's running your code. Machines often have several Pythons, and a bare pip may belong to a different one. Fix it →
• ZeroDivisionError: division by zero Python
  Division or modulo by zero. Fix it →
• RecursionError: maximum recursion depth exceeded Python
  The recursion depth passed sys.getrecursionlimit(), which is 1000 by default on CPython. Fix it →
• ReferenceError: Cannot access 'x' before initialization JavaScript
  This is the temporal dead zone: let, const and class declarations are hoisted but stay uninitialized until the declaration line runs, and touching them before then throws. Fix it →
• ReferenceError: x is not defined JavaScript
  The name was never declared anywhere the current code can see. Fix it →
• SyntaxError: Unexpected token JavaScript
  The parser hit a character it couldn't fit into valid grammar. The reported position is often after the real mistake. Fix it →
• RangeError: Maximum call stack size exceeded JavaScript
  Too many function calls were nested at once. Fix it →
• Uncaught (in promise) JavaScript
  A promise rejected and nothing handled the rejection. Browsers log it after Uncaught (in promise); since Node.js v15 an unhandled rejection is raised as an uncaught exception and stops the process. Fix it →
• TypeError (Python) Python
  A TypeError means an operation was applied to an object of inappropriate type. Fix it →
• Python exception Python
  This is a Python traceback. The last line names the exception type and message. Fix it →
• TypeError (JavaScript) JavaScript
  A JavaScript TypeError means the value exists but is the wrong kind for the operation. Fix it →