Error map
TS2451: Cannot redeclare block-scoped variable TypeScript: error TS2451: Cannot redeclare block-scoped variable 'name'.
TypeScript · 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)
ReferenceError: x is not defined
Code refers to a variable or function name that doesn’t exist in the current scope.
SyntaxError: Identifier 'x' has already been declared
The same let/const/class name was declared twice in the same scope.
ReferenceError: Cannot access 'x' before initialization
A let/const/class was used before its declaration line ran (temporal dead zone) — often a circular import.
TypeScript: error TS2305: Module '"./utils"' has no exported member 'helper'.
You imported a named export that the module doesn't export.
TypeScript: error TS1259: Module '"express"' can only be default-imported using the 'esModuleInterop' flag
You default-import a CommonJS module that uses `export =`, but `esModuleInterop` isn't enabled.
TypeScript: error TS2300: Duplicate identifier 'Foo'.
The same name is declared twice in the same scope (or in merged global declarations).
TypeScript: error TS2393: Duplicate function implementation.
A function with the same name/signature is implemented more than once in the same scope.
TypeScript: error TS2403: Subsequent variable declarations must have the same type. Variable 'x' must be of type 'string', but here has type 'number'.
A `var` was redeclared with a different type (or global declarations conflict).
TypeScript: error TS1208: 'index.ts' cannot be compiled under '--isolatedModules' because it is considered a global script file. Add an import, export, or an empty 'export {}' statement
With `isolatedModules`, every file must be a module (have an import or export).
TypeScript: error TS2614: Module '"./Button"' has no exported member 'Button'. Did you mean to use 'import Button from "./Button"' instead?
You used a named import for something that's a default export (or reverse).
TypeScript: error TS1192: Module '"./utils"' has no default export.
You used `import x from "./mod"` but the module only has named exports.
TypeScript: error TS2307: Cannot find module './App.vue' or its corresponding type declarations.
TypeScript doesn't know what a `.vue` import is without a shim or Volar/`vue-tsc`.
Two steps away (36)
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…
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…).
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 token '<' (HTML served instead of JavaScript)
The browser loaded a .js file but received HTML (an error page or the SPA index.html).
SyntaxError: Unexpected end of input
The parser reached the end of the code (or JSON) while still expecting more — a missing } ) ] or empty JSON.
SyntaxError: missing ) after argument list
A function call’s parentheses are unbalanced — often an unescaped quote or a missing comma/plus.
TypeError: x is not a constructor
new was used with something that isn’t a class/constructor — usually a wrong import.
MySQL ERROR 1046 (3D000): No database selected
A query referenced tables without a database selected (no USE and no db in the connection).
MySQL ERROR 1153 (08S01): Got a packet bigger than 'max_allowed_packet' bytes
A single statement or row exceeded max_allowed_packet — big BLOBs, huge INSERTs or large dump lines.
TS2307: Cannot find module 'x' or its corresponding type declarations.
TypeScript can’t resolve the import — the package isn’t installed, the path alias isn’t configured, or there are no types.
TypeScript: error TS2792: Cannot find module 'x'. Did you mean to set the 'moduleResolution' option to 'nodenext', or to add aliases to the 'paths' option?
TypeScript can't resolve a package because `moduleResolution` doesn't match how the package exports (package `exports` map) or pa…
TypeScript: error TS5095
`moduleResolution: "bundler"` needs a compatible `module` setting.
Error [ERR_REQUIRE_ESM]: require() of ES Module not supported
CommonJS code used `require()` on a package that is ES-module-only (node-fetch 3, chalk 5, nanoid 4, got 12…).
SyntaxError: Cannot use import statement outside a module
An `import` statement ran in a context treated as CommonJS (Node without "type": "module", a browser script without type="module"…
TypeError [ERR_IMPORT_ATTRIBUTE_MISSING]: Module needs an import attribute of "type: json"
An ES module imported a .json file without the required import attribute.
TS2304: Cannot find name 'x'.
TypeScript doesn’t know an identifier — a missing import, missing type definitions (e.g. for Node or Jest globals), or a typo.
TypeScript: error TS1005: ';' expected.
The parser hit a syntax error — missing punctuation, mismatched brackets, or an unsupported syntax for your TypeScript version.
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…
TypeScript: error TS2349: This expression is not callable. Type 'X' has no call signatures.
You called something TypeScript believes isn't a function (a union without compatible signatures, a module namespace, an object).
TypeScript: error TS2366: Function lacks ending return statement and return type does not include 'undefined'.
A function with a declared return type can reach its end without returning on some path.
TypeScript: error TS2554: Expected 2 arguments, but got 1.
A call passes too few or too many arguments.
TypeError: Assignment to constant variable.
Code reassigned a variable declared with const.
TS2322: Type 'X' is not assignable to type 'Y'
You assigned a value whose type doesn’t match the declared type of the variable, property or return value.
TypeScript: error TS4023: Exported variable 'x' has or is using name 'Foo' from external module "..." but cannot be named. / TS2742: The inferred type cannot be named without a reference
With `declaration: true`, TypeScript can't write the inferred type into `.d.ts` because it refers to a type it can't import by na…
Error [ERR_PACKAGE_PATH_NOT_EXPORTED]: Package subpath './x' is not defined by "exports"
You imported a deep path inside a package that its package.json "exports" field doesn’t expose.
TypeScript: error TS2531: Object is possibly 'null'.
You used a value that can be `null` without checking it first (strictNullChecks).
TypeScript: error TS2551: Property 'lenght' does not exist on type 'string'. Did you mean 'length'?
A property name is misspelled (TypeScript suggests the closest valid one).
TypeError: Router.use() requires a middleware function but got a Object
app.use()/router.use() received an object instead of a function — usually a router module that wasn’t exported.
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.
Next.js: Module not found: Can't resolve '@/components/Button' / 'lodash' in '/app/src'
Webpack/Turbopack couldn't resolve an import — wrong path/alias, missing dependency or case mismatch.
TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".ts"
Node tried to run a TypeScript file as ESM without a TypeScript loader.
TS18048: 'x' is possibly 'undefined'. (TS2532: Object is possibly 'undefined'.)
TypeScript requires you to handle the case where a value may be undefined before using it.
Next.js: Failed to compile. ./src/app/page.tsx:15:9 Type error: Type 'string | undefined' is not assignable to type 'string'
TypeScript type checking failed during `next build`, which blocks the deployment.
TS7016: Could not find a declaration file for module 'x'. 'x.js' implicitly has an 'any' type.
The JavaScript package has no TypeScript types bundled and no @types package installed.
TS2339: Property 'x' does not exist on type 'Y'.
TypeScript’s type for the object doesn’t include that property.
TS2345: Argument of type 'string | undefined' is not assignable to parameter of type 'string'.
A value’s type doesn’t match the function parameter — commonly a possibly-undefined value passed where a definite one is required.
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