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typescript

TS1219: Experimental support for decorators must be enabled in 'experimentalDecorators'

You're using decorator syntax (@ before a class, method, or property) but TypeScript's experimental decorator support isn't enabled in tsconfig.json. Decorators are common in Angular, NestJS, TypeORM, and MobX.

Common causes

Using class decorators (@Component, @Injectable, @Entity) without enabling experimentalDecorators
Following a framework tutorial that assumes experimental decorators are already on
A new tsconfig.json was generated but framework-specific options weren't added
tsconfig.json was reset or overwritten and the decorator option was lost

How to fix it

Add to tsconfig.json compilerOptions: { "experimentalDecorators": true }
Also add emitDecoratorMetadata: true if using dependency injection (Angular, NestJS)
Use the framework's recommended tsconfig template — Angular CLI and NestJS CLI generate a correct config
For TypeScript 5.0+, check if your framework supports the new standard decorators proposal

Example

@Injectable()
class UserService { }
// error TS1219: Experimental support for decorators is a feature that is subject to change in a future release. Set the 'experimentalDecorators' option in your 'tsconfig' or 'jsconfig' to remove this warning.

Using NestJS @Injectable() decorator without experimentalDecorators in tsconfig.json

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