TypeScript New Added 9 September 2026

TypeScript: Cannot redeclare block-scoped variable 'name'

A file with no import or export is treated as a script, not a module, so its top level declarations land in the global scope and collide with the DOM library or with another file. The name in the message is usually something like name, event or status that already exists on window.

Quick fix

Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.

Quick fix

// Make the file a module. One empty export is enough
export {};

// A Node project should not be pulling in the DOM globals
{ "compilerOptions": { "lib": ["ES2022"], "types": ["node"] } }

# Two copies of @types/node declare everything twice
npm ls @types/node
npm dedupe

# Old build output being type checked alongside the source
{ "exclude": ["dist", "build", "node_modules"] }

# See which files the compiler actually included
npx tsc --listFiles | grep -v node_modules

How to diagnose TypeScript errors

TypeScript errors are the compiler describing a mismatch between what you declared and what you did. Nearly all of them fall into assignability (this shape is not that shape), missing declarations (a JavaScript package with no types), or strict null checks (a value can be undefined on a path you did not handle). Casting with as or any silences the message without fixing the underlying mismatch, which usually reappears at runtime.

If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.

Read the error from the innermost "Types of property X are incompatible" line outward. That nested line names the actual mismatch.
For missing declarations, try npm i -D @types/<pkg> first; if none exists, write a minimal .d.ts rather than reaching for any.
Narrow rather than assert. A type guard, an in check, or an early return preserves safety where as discards it.
Use tsc --noEmit --pretty to check the whole project; editors sometimes use a different TypeScript version than the build.
Check strict, skipLibCheck and moduleResolution in tsconfig when errors appear only in CI or only in the editor.

Tools worth reaching for

tsc --noEmit
ts-node / tsx
@types/* packages
typescript-eslint
editor TS version selector

Authoritative references

Primary documentation for this error, worth reading before applying any fix in production.

typescriptlang.org

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