EC
TS1290
TypeScriptERRORNotableSyntaxHIGH confidence

'X' resolves to a type-only declaration and must be marked type-only in this ...

Production Risk

Build will fail; resolve before shipping.

What this means

A syntax error (TS1290): 'X' resolves to a type-only declaration and must be marked type-only in this file before re-exporting when 'X' is enabled. Consider using 'export type X as default }'.. This diagnostic is emitted by the TypeScript compiler when 'X' resolves to a type-only declaration and must be marked type-only in this file before re-exporting when 'X' is enabled. Consider using 'export type X as default }'..

Why it happens
  1. 1Incorrect TypeScript syntax or type usage
  2. 2Type mismatch between declared and actual value
How to reproduce

TypeScript compiler reports TS1290 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS1290
// 'X' resolves to a type-only declaration and must be marked type-only in this file before re-exporting when 'X' is enabled. Consider using 'export type X as default }'.

expected output

error TS1290: 'X' resolves to a type-only declaration and must be marked type-only in this file before re-exporting when 'X' is enabled. Consider using 'export type X as default }'.

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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