EC
TS1433
TypeScriptERRORNotableSyntaxHIGH confidence

Neither decorators nor modifiers may be applied to 'this' parameters.

Production Risk

Build will fail; resolve before shipping.

What this means

A syntax error (TS1433): Neither decorators nor modifiers may be applied to 'this' parameters.. This diagnostic is emitted by the TypeScript compiler when neither decorators nor modifiers may be applied to 'this' parameters..

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 TS1433 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS1433
// Neither decorators nor modifiers may be applied to 'this' parameters.

expected output

error TS1433: Neither decorators nor modifiers may be applied to 'this' parameters.

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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