EC
TS6203
TypeScriptERRORNotableConfigHIGH confidence

'X' was also declared here.

Production Risk

Build will fail; resolve before shipping.

What this means

A compiler configuration error (TS6203): 'X' was also declared here.. This diagnostic is emitted by the TypeScript compiler when 'X' was also declared here..

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

TypeScript compiler reports TS6203 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS6203
// 'X' was also declared here.

expected output

error TS6203: 'X' was also declared here.

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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