EC
TS1270
TypeScriptERRORNotableSyntaxHIGH confidence

Decorator function return type 'X' is not assignable to type 'X'.

Production Risk

Build will fail; resolve before shipping.

What this means

A syntax error (TS1270): Decorator function return type 'X' is not assignable to type 'X'.. This diagnostic is emitted by the TypeScript compiler when decorator function return type 'X' is not assignable to type 'X'..

Why it happens
  1. 1The value type does not match the declared or expected type
  2. 2A type narrowing or assertion is needed
How to reproduce

TypeScript compiler reports TS1270 during type checking.

trigger — this will error
trigger — this will error
// Triggers TS1270
// Decorator function return type 'X' is not assignable to type 'X'.

expected output

error TS1270: Decorator function return type 'X' is not assignable to type 'X'.

Fix

Fix the type mismatch

WHEN When the value type does not match the target type

Fix the type mismatch
// Add a type assertion if you are certain of the type
const value = someValue as ExpectedType;
// Or fix the source type to match

Why this works

Type assertions bypass type checking; prefer fixing the underlying type mismatch.

Sources
Official documentation ↗

TypeScript Compiler Diagnostics

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