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TS2300: Duplicate identifier - in CI

·Latchkey

tsc found the same identifier declared more than once in a way that conflicts.

What this error means

Type-checking fails with TS2300 naming the duplicated identifier, frequently from two copies of a @types package.

tsc
node_modules/@types/node/globals.d.ts(72,13): error TS2300: Duplicate identifier 'RequestInit'.

Common causes

How to fix it

Deduplicate type packages

  1. Find duplicate @types in the tree and dedupe to one version
shell
npm ls @types/node

Scope the included types

  1. Pin compilerOptions.types to only the packages you need
  2. Adjust lib so it does not duplicate a @types global
tsconfig.json
{
  "compilerOptions": {
    "types": ["node"]
  }
}

How to prevent it

  • Keep one version of each @types package and use a focused types allowlist to avoid global collisions.

Frequently asked questions

What causes "TS2300 duplicate identifier"?
Type-checking fails with TS2300 naming the duplicated identifier, frequently from two copies of a @types package.
How do I fix TS2300 duplicate identifier?
Deduplicate type packages

Related guides

TS2451: Cannot redeclare block-scoped variable - in CIFix "error TS2451: Cannot redeclare block-scoped variable 'x'" when tsc runs in CI - a duplicate declaration… TS18049: Value is possibly null or undefined - in CIFix "error TS18049: 'x' is possibly 'null' or 'undefined'" when tsc runs in CI - narrow a T | null | undefine… TS2304: Cannot find name - in CIFix "error TS2304: Cannot find name 'x'" when tsc runs in CI - a missing import, a missing lib/types entry, o…

References

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