EC
TS1237
TypeScriptERRORNotableSyntaxHIGH confidence

The return type of a parameter decorator function must be either 'void' or 'a...

Production Risk

Build will fail; resolve before shipping.

What this means

A syntax error (TS1237): The return type of a parameter decorator function must be either 'void' or 'any'.. This diagnostic is emitted by the TypeScript compiler when the return type of a parameter decorator function must be either 'void' or 'any'..

Why it happens
  1. 1A decorator is applied incorrectly or to an unsupported target
  2. 2The 'experimentalDecorators' flag may need to be enabled
How to reproduce

TypeScript compiler reports TS1237 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS1237
// The return type of a parameter decorator function must be either 'void' or 'any'.

expected output

error TS1237: The return type of a parameter decorator function must be either 'void' or 'any'.

Fix

Enable experimentalDecorators

WHEN Using legacy decorator syntax

Enable experimentalDecorators
// tsconfig.json
{
  "compilerOptions": {
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true
  }
}

Why this works

Decorators require the 'experimentalDecorators' flag; TypeScript 5.0+ also supports the TC39 Stage 3 decorator proposal without the flag.

What not to do

✕ Suppress with @ts-ignore instead of fixing the type

ts-ignore hides real type errors and makes refactoring unsafe.

Sources
Official documentation ↗

TypeScript Compiler Diagnostics

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