EC
TS9011
TypeScriptERRORNotableTypeHIGH confidence

Parameter must have an explicit type annotation with --isolatedDeclarations.

Production Risk

Build will fail; resolve before shipping.

What this means

A TypeScript diagnostic (TS9011): Parameter must have an explicit type annotation with --isolatedDeclarations.. This diagnostic is emitted by the TypeScript compiler when parameter must have an explicit type annotation with --isolatedDeclarations..

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

TypeScript compiler reports TS9011 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS9011
// Parameter must have an explicit type annotation with --isolatedDeclarations.

expected output

error TS9011: Parameter must have an explicit type annotation with --isolatedDeclarations.

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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