Demystifying the Mysterious Error: “Cannot Import Shared Enum Type into NestJS Project”

Are you tired of banging your head against the wall, trying to figure out why you can’t import that shared enum type into your NestJS project? Well, you’re in luck because we’re about to dive deep into the world of enums, modules, and imports to uncover the solution to this frustrating error.

What are Enums in TypeScript?

Before we dive into the issue at hand, let’s take a step back and understand what enums are in TypeScript. Enums, short for enumerations, are a way to define a set of named values. They allow you to define a set of named constants, making your code more readable and maintainable.

enum Colors {
  Red,
  Green,
  Blue
}

In the above example, we’ve defined an enum called `Colors` with three possible values: `Red`, `Green`, and `Blue`. Enums are particularly useful when you need to define a set of distinct values that have a specific meaning in your application.

Shared Enums in NestJS

In a NestJS project, enums can be shared across multiple modules by defining them in a separate file and importing them where needed. This is where things can get a bit tricky, and we’ll explore the reasons behind the “Cannot import shared enum type into NestJS project” error.

The Problem: Cannot Import Shared Enum Type

Let’s say you have a shared enum file called `enums.ts` with the following content:

export enum ApiStatus {
  OK,
  ERROR,
  PENDING
}

You try to import this enum in one of your NestJS modules, say `users.module.ts`:

import { ApiStatus } from './../../shared/enums';

@Module({
  imports: [],
  controllers: [UsersController],
  providers: [UsersService]
})
export class UsersModule {}

However, when you try to compile your project, you’re greeted with the dreaded error:

error TS2307: Cannot find module './../../shared/enums' or its corresponding type declarations.

What’s going on here?

Understanding the Error

The error message is trying to tell us that the TypeScript compiler can’t find the `enums` module or its type declarations. This is because enums, by default, are not exported as modules. Instead, they’re exported as a type.

To understand why this is the case, let’s take a look at the compiled JavaScript code for our enum:

var ApiStatus;
(function (ApiStatus) {
  ApiStatus[ApiStatus["OK"] = 0] = "OK";
  ApiStatus[ApiStatus["ERROR"] = 1] = "ERROR";
  ApiStatus[ApiStatus["PENDING"] = 2] = "PENDING";
})(ApiStatus || (ApiStatus = {}));
exports.ApiStatus = ApiStatus;

Notice that the compiled JavaScript code doesn’t create a module. Instead, it creates a type called `ApiStatus` and assigns it to the `exports` object. This is why we can’t import the enum as a module.

Solution 1: Importing Enums Correctly

So, how do we import enums correctly in our NestJS project? The answer lies in the way we import and use enums in our TypeScript code.

import type { ApiStatus } from './../../shared/enums';

@Module({
  imports: [],
  controllers: [UsersController],
  providers: [UsersService]
})
export class UsersModule {
  constructor(private readonly usersService: UsersService) {}

  async someMethod() {
    const status: ApiStatus = ApiStatus.OK;
    // ...
  }
}

Notice the `import type` syntax? This tells TypeScript that we’re importing a type, not a module. By using `import type`, we can import the enum type and use it in our code.

Solution 2: Creating a Utility Module

Another approach to sharing enums across multiple modules is to create a utility module that exports the enum as a value.

// shared/utils.enum.ts
export enum ApiStatus {
  OK,
  ERROR,
  PENDING
}

export const apiStatusValues = Object.values(ApiStatus);

In this example, we’ve created a utility module that exports both the `ApiStatus` enum and an array of its values using `Object.values()`.

import { apiStatusValues } from './../../shared/utils.enum';

@Module({
  imports: [],
  controllers: [UsersController],
  providers: [UsersService]
})
export class UsersModule {
  constructor(private readonly usersService: UsersService) {}

  async someMethod() {
    const status = apiStatusValues[0]; // ApiStatus.OK
    // ...
  }
}

By creating a utility module, we can share the enum values across multiple modules, making it easier to use them in our application.

Conclusion

In conclusion, the “Cannot import shared enum type into NestJS project” error is a common issue that arises from the way enums are exported and imported in TypeScript. By understanding the difference between importing modules and types, we can correctly import and use shared enums in our NestJS project.

Remember, when working with shared enums, always use the `import type` syntax to import the enum type, or create a utility module that exports the enum values as a value.

By following these simple yet effective solutions, you’ll be well on your way to sharing enums across multiple modules in your NestJS project.

Solution	Description
Solution 1: Importing Enums Correctly	Use the `import type` syntax to import the enum type and use it in your code.
Solution 2: Creating a Utility Module	Create a utility module that exports the enum values as a value, making it easier to share across multiple modules.

We hope this article has helped you understand and overcome the “Cannot import shared enum type into NestJS project” error. Happy coding!

• TypeScript Enums Documentation
• NestJS Modules Documentation
• TypeScript Modules Documentation

1. UNDERSTANDING ENUMS IN TYPESCRIPT
2. SHARED ENUMS IN NESTJS
3. THE PROBLEM: CANNOT IMPORT SHARED ENUM TYPE
4. UNDERSTANDING THE ERROR
5. SOLUTION 1: IMPORTING ENUMS CORRECTLY
6. SOLUTION 2: CREATING A UTILITY MODULE
7. CONCLUSION

Frequently Asked Question

Stuck with importing shared enum types into your NestJS project? We’ve got you covered! Check out these frequently asked questions and their answers to get back on track.