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Proto Enums ​

Proto files commonly use enum, which generates non-erasable TypeScript. This page describes the workaround and alternatives.

The Problem ​

protoc-gen-es generates TypeScript enum declarations for proto enums:

protobuf
// In your .proto file
enum OrderStatus {
  ORDER_STATUS_UNSPECIFIED = 0;
  ORDER_STATUS_PENDING = 1;
  ORDER_STATUS_SHIPPED = 2;
}

This generates:

typescript
// Generated code -- NOT erasable
export enum OrderStatus {
  UNSPECIFIED = 0,
  PENDING = 1,
  SHIPPED = 2,
}

Node.js cannot execute this directly because enum generates runtime code.

The Two-Step Workaround ​

  1. Generate TypeScript to a temporary directory (gen-ts/)
  2. Compile with tsc to produce JavaScript in gen/
json
{
  "scripts": {
    "build:proto": "protoc -I proto --plugin=protoc-gen-es=./node_modules/.bin/protoc-gen-es --es_out=gen-ts --es_opt=target=ts proto/*.proto",
    "build:proto:compile": "tsc -p tsconfig.gen.json",
    "build:proto:all": "pnpm build:proto && pnpm build:proto:compile"
  }
}

Create tsconfig.gen.json for the compilation step:

json
{
  "compilerOptions": {
    "target": "esnext",
    "module": "nodenext",
    "moduleResolution": "nodenext",
    "declaration": true,
    "outDir": "gen",
    "rootDir": "gen-ts"
  },
  "include": ["gen-ts/**/*.ts"]
}

Avoiding the Workaround ​

If you control your proto definitions, you can avoid enum entirely:

protobuf
// Instead of enum, use int32 constants
message Order {
  int32 status = 1;
  // Constants defined in documentation:
  // 0 = UNSPECIFIED
  // 1 = PENDING
  // 2 = SHIPPED
}

Then define constants in TypeScript:

typescript
const OrderStatus = {
  UNSPECIFIED: 0,
  PENDING: 1,
  SHIPPED: 2,
} as const;

type OrderStatus = typeof OrderStatus[keyof typeof OrderStatus];

Future improvement

This workaround is temporary. When Node.js adds native enum support (or protoc-gen-es offers an option to generate as const objects), the two-step process will no longer be needed.