EC
TS1278
TypeScriptERRORNotableSyntaxHIGH confidence

The runtime will invoke the decorator with X arguments, but the decorator exp...

Production Risk

Build will fail; resolve before shipping.

What this means

A syntax error (TS1278): The runtime will invoke the decorator with X arguments, but the decorator expects X.. This diagnostic is emitted by the TypeScript compiler when the runtime will invoke the decorator with X arguments, but the decorator expects X..

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 TS1278 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS1278
// The runtime will invoke the decorator with X arguments, but the decorator expects X.

expected output

error TS1278: The runtime will invoke the decorator with X arguments, but the decorator expects X.

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.

Sources
Official documentation ↗

TypeScript Compiler Diagnostics

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