EC
TS5085
TypeScriptERRORNotableConfigHIGH confidence

A tuple member cannot be both optional and rest.

Production Risk

Build will fail; resolve before shipping.

What this means

A compiler configuration error (TS5085): A tuple member cannot be both optional and rest.. This diagnostic is emitted by the TypeScript compiler when a tuple member cannot be both optional and rest..

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

TypeScript compiler reports TS5085 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS5085
// A tuple member cannot be both optional and rest.

expected output

error TS5085: A tuple member cannot be both optional and rest.

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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