Here is the tsconfig.json:

{
  "compilerOptions": {
    "module": "commonjs",
    "declaration": true,
    "removeComments": true,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "allowSyntheticDefaultImports": true,
    "sourceMap": true,
    "target": "es2017",
    "outDir": "./js",
    "rootDir": "./src",
    "baseUrl": "./",
    "incremental": true,
  }
}

here is the tsconfig.build.json:

{
  "extends": "./tsconfig.json",
  "exclude": ["node_modules", "test", "dist", "**/*spec.ts"]
}

Here is the package.json:

{
  "name": "",
  "version": "0.0.1",
  "description": "",
  "author": "",
  "private": true,
  "license": "UNLICENSED",
  "scripts": {
    "build": "tsc --outDir js --downlevelIteration --target es5 src/main.ts",
    "format": "prettier --write "src/**/*.ts" "test/**/*.ts"",
    "lint": "eslint "{src}/**/*.ts" --fix",
    "test": "jest",
    "test:watch": "jest --watch",
    "test:cov": "jest --coverage",
    "test:debug": "node --inspect-brk -r tsconfig-paths/register -r ts-node/register node_modules/.bin/jest --runInBand",
    "test:e2e": "jest --config ./test/jest-e2e.json"
  },
  "dependencies": {
    "@types/prompts": "^2.4.9",
    "class-transformer": "^0.5.1",
    "class-validator": "^0.14.1",
    "commander": "^12.1.0",
    "kleur": "^4.1.5",
    "prompts": "^2.4.2",
    "reflect-metadata": "^0.1.13",
    "rimraf": "^3.0.2"
  },
  "devDependencies": {
    "@types/express": "^4.17.13",
    "@types/node": "^16.0.0",
    "@typescript-eslint/eslint-plugin": "^5.0.0",
    "@typescript-eslint/parser": "^5.0.0",
    "eslint": "^8.0.1",
    "eslint-config-prettier": "^8.3.0",
    "eslint-plugin-prettier": "^4.0.0",
    "prettier": "^2.3.2",
    "source-map-support": "^0.5.20",
    "ts-loader": "^9.2.3",
    "ts-node": "^10.0.0",
    "tsconfig-paths": "4.1.0",
    "typescript": "^4.7.4"
  }
}

I’m getting the error in the title when I run npm run build .

Full error:

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.

I tried updating node and npm.

~ node -v
~ v20.14.0

~ npm -v
~ 10.7.0

~ tsc --version
Version 5.4.5

What helped to compile the code without errors was adding the --experimentalDecorators option. But why? What is wrong here?