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Angular

Solve NG6002 Error: NgModule Import Not Resolved

By Filip on 10/05/2024

This article provides a solution for the Angular error NG6002 which occurs when a module imported in AppModule cannot be resolved to an NgModule class.

Solve NG6002 Error: NgModule Import Not Resolved

Table of Contents

Introduction

The error message "error NG6002: Appears in the NgModule.imports of AppModule, but could not be resolved to an NgModule class" is a common issue in Angular development. It means you're trying to import something into your AppModule's imports array that isn't an NgModule. This article will guide you through the common causes of this error and how to fix them, including typos, incorrect imports, missing installations, circular dependencies, AOT compilation issues, outdated Angular versions, and IDE/cache problems. We'll also illustrate the solution with a practical example of importing Angular Material components.

Step-by-Step Guide

The error message "error NG6002: Appears in the NgModule.imports of AppModule, but could not be resolved to an NgModule class" usually pops up in Angular development when you try to import something into the imports array of your AppModule that isn't actually an NgModule. Here's a breakdown of common causes and how to fix them:

1. Typos and Incorrect Imports

  • Double-check your import paths: Make sure the path to the module you're importing is correct. A small typo can easily cause this error.

  • Verify module names: Ensure the module name you're importing matches the actual module class name.

    // Incorrect (assuming MyModule is the class name)
import { MyModules } from './my-module/my-module.module'; 

// Correct
import { MyModule } from './my-module/my-module.module';

2. Missing or Incorrect Installations

  • Install the module: If you're using a third-party library, make sure it's installed in your project:

    npm install <library-name>

  • Check package.json: Verify that the library is listed as a dependency in your package.json file.

3. Circular Dependencies

  • Identify the loop: Circular dependencies occur when two or more modules try to import each other, creating a loop. Analyze your imports to find the source of the cycle.
  • Refactor your code: Break the circular dependency by:
    • Moving shared components, services, or directives to a separate module that both dependent modules can import.
    • Using forward references (using forwardRef in providers) if absolutely necessary.

4. AOT Compilation Issues

  • Build without AOT: Try building your project without Ahead-of-Time (AOT) compilation to see if the error persists:

    ng build --prod=false

  • Investigate AOT-specific problems: If the error only occurs during AOT compilation, it might indicate an issue with how your library or code is structured for AOT. Check the library's documentation for AOT compatibility or potential workarounds.

5. Outdated Angular Versions

  • Update Angular and CLI: Ensure you're using the latest versions of Angular and the Angular CLI. Older versions might have compatibility issues.

    ng update @angular/cli @angular/core

6. IDE and Cache Issues

  • Restart your IDE: Sometimes, your IDE's cache can cause problems. Restarting it might resolve the issue.
  • Clear the Angular cache: Delete the node_modules folder and the package-lock.json file, then run npm install to reinstall your dependencies.

Example: Importing Angular Material

Let's say you're trying to import Angular Material components and get this error. Here's how you'd fix it:

// app.module.ts

// Incorrect: Trying to import a component directly
import { MatButtonModule } from '@angular/material/button'; 

// Correct: Import the Material module
import { MatButtonModule } from '@angular/material/button';
import { MatCardModule } from '@angular/material/card'; 

@NgModule({
  imports: [
    // ... other imports
    MatButtonModule,
    MatCardModule
  ],
  // ...
})
export class AppModule { }

Remember: Always carefully review the documentation of the library you're trying to import for specific installation and import instructions.

Code Example

This JavaScript code demonstrates common reasons for the "error NG6002" in Angular applications. It highlights issues like typos in import statements, missing library installations, circular dependencies, and potential problems with AOT compilation or outdated Angular versions. The code includes an intentional typo importing "BrowserModulee" and a commented-out import for "MatButtonModule" to illustrate these issues. It suggests correcting the typo and installing Angular Material to resolve the errors in this specific example. The code emphasizes consulting library documentation for specific installation and import instructions.

// Example demonstrating common causes and fixes for "error NG6002"

// app.module.ts

// 1. Typos and Incorrect Imports
// import { BrowserModule } from '@angular/platform-browser'; // Correct
import { BrowserModulee } from '@angular/platform-browser'; // Incorrect - Typo in module name

// 2. Missing or Incorrect Installations
// Make sure the library is installed (e.g., npm install @angular/material)
// import { MatButtonModule } from '@angular/material/button'; // Will cause error if not installed

// 3. Circular Dependencies (Illustrative Example)
// module-a.module.ts
// import { ModuleB } from './module-b/module-b.module'; // Creates a circular dependency if ModuleB imports ModuleA

// 4. AOT Compilation Issues (Usually library-specific, check library documentation)

// 5. Outdated Angular Versions (Update using ng update)

@NgModule({
  declarations: [AppComponent],
  imports: [
    BrowserModulee, // This will cause the NG6002 error due to the typo
    // MatButtonModule // Uncommenting this without installation will cause the error
  ],
  bootstrap: [AppComponent],
})
export class AppModule {}

Explanation:

  • Typo: The code intentionally includes a typo (BrowserModulee) to demonstrate how a simple mistake in the import statement can lead to the NG6002 error.
  • Missing Installation: The commented-out MatButtonModule import shows how attempting to import from a library that hasn't been installed will cause the error.
  • Circular Dependency: The comment about module-a.module.ts and module-b.module.ts illustrates how circular dependencies can lead to this error, though it doesn't provide a full working example to avoid complexity.
  • AOT and Outdated Versions: These are more situational and often require specific debugging based on the library or Angular version being used.

To Fix the Errors in this Example:

  1. Correct the typo: Change BrowserModulee to BrowserModule.
  2. Install the missing library: Uncomment the MatButtonModule line and run npm install @angular/material @angular/cdk to install Angular Material.

This example provides a practical illustration of the common causes of the NG6002 error and how to address them. Remember to consult the documentation of specific libraries you're using for detailed installation and import instructions.

Additional Notes

  • Consider using a linter: Linters like TSLint or ESLint can help catch typos, incorrect import paths, and other potential issues early on.
  • Inspect the error message closely: The error message often provides clues about the problematic import. Pay attention to the file path and module name mentioned.
  • Use your IDE's features: Most modern IDEs offer auto-import functionality and error highlighting, which can help prevent and identify incorrect imports.
  • When working with third-party libraries, consult their documentation: The documentation usually provides clear instructions on installation and how to import the necessary modules.
  • If using a shared module, ensure it's imported in AppModule or any other modules that require its components/services: Missing imports in shared modules can lead to the NG6002 error in dependent modules.
  • For complex scenarios, consider creating a minimal reproduction: If you're struggling to find the cause, create a minimal Angular project that reproduces the error and share it on platforms like Stack Overflow or GitHub for assistance.

Summary

This error means you're trying to import something into an NgModule's imports array that isn't actually an NgModule. Here's a breakdown of common causes and fixes:

Cause Solution
Typos/Incorrect Imports Double-check import paths and module names for accuracy.
Missing/Incorrect Installations Install the library (npm install <library-name>) and verify it's in package.json.
Circular Dependencies Identify the import loop and refactor by moving shared code to a separate module or using forwardRef.
AOT Compilation Issues Build without AOT (ng build --prod=false) and investigate AOT-specific problems if the error persists.
Outdated Angular Versions Update Angular and CLI (ng update @angular/cli @angular/core).
IDE/Cache Issues Restart your IDE or clear the Angular cache (rm -rf node_modules package-lock.json && npm install).

Key Point: Always consult the documentation of the library you're importing for specific instructions.

Example (Angular Material):

// Incorrect: Importing a component directly
import { MatButtonModule } from '@angular/material/button'; 

// Correct: Importing the Material module
import { MatButtonModule } from '@angular/material/button';

Conclusion

By addressing these common causes, you can effectively resolve the "error NG6002" and ensure the smooth functioning of your Angular applications. Remember to leverage your IDE's features, consult library documentation, and consider creating minimal reproductions for complex scenarios to streamline the debugging process.

References

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