EC
TS6138
TypeScriptERRORNotableConfigHIGH confidence

Property 'X' is declared but its value is never read.

Production Risk

Build will fail; resolve before shipping.

What this means

A compiler configuration error (TS6138): Property 'X' is declared but its value is never read.. This diagnostic is emitted by the TypeScript compiler when property 'X' is declared but its value is never read..

Why it happens
  1. 1A code path that should return a value returns never instead, or vice versa
How to reproduce

TypeScript compiler reports TS6138 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS6138
// Property 'X' is declared but its value is never read.

expected output

error TS6138: Property 'X' is declared but its value is never read.

Fix

Fix the tsconfig.json option

WHEN When a compiler option is invalid or missing

Fix the tsconfig.json option
// tsconfig.json
{
  "compilerOptions": {
    // Review and correct the flagged option
  }
}
// Run: npx tsc --showConfig to see effective config

Why this works

TypeScript validates tsconfig.json options; check the official tsconfig reference for valid values.

Sources
Official documentation ↗

TypeScript Compiler Diagnostics

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