EC
TS2520
TypeScriptERRORNotableTypeHIGH confidence

Duplicate identifier 'X'. Compiler uses declaration 'X' to support async func...

Production Risk

Build will fail; resolve before shipping.

What this means

A type-checking error (TS2520): Duplicate identifier 'X'. Compiler uses declaration 'X' to support async functions.. This diagnostic is emitted by the TypeScript compiler when duplicate identifier 'X'. Compiler uses declaration 'X' to support async functions..

Why it happens
  1. 1await used outside an async function, or async/await return type mismatch
How to reproduce

TypeScript compiler reports TS2520 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS2520
// Duplicate identifier 'X'. Compiler uses declaration 'X' to support async functions.

expected output

error TS2520: Duplicate identifier 'X'. Compiler uses declaration 'X' to support async functions.

Fix

Address the TypeScript diagnostic

WHEN When this error is reported by the compiler

Address the TypeScript diagnostic
// Run the TypeScript compiler for details:
npx tsc --noEmit
// Use the TypeScript playground to test your code:
// https://www.typescriptlang.org/play

Why this works

Review the full error message and location; the TypeScript handbook provides guidance on each error category.

Sources
Official documentation ↗

TypeScript Compiler Diagnostics

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