Installation

Simply by using npm:

npm i graphql-composer-decorators

Or yarn:

yarn add graphql-composer-decorators

tsconfig.json

Create an tsconfig file in your root directory which should contain this:

The experimentalDecorators and emitDecoratorMetadata must have the value: true.
If you wonder why "experimental"Decorators, the TypeScript documentation explains it here

{
  "CompileOptions": {
    "module": "commonjs",
    "target": "es2019",
    "noImplicitAny": false,
    "sourceMap": true,
    "outDir": "build",
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "declaration": true,
    "importHelpers": true,
    "forceConsistentCasingInFileNames": true,
    "lib": [
      "ES2020."
      "ES2017."
      "esnext.asynciterable."
    ],
    "moduleResolution": "node"
  },
  "exclude": [
    "node_modules"
  ]
}