Rollup can't resolve my typings file when trying to build

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05-10-2024

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"Rollup can't resolve my typings file": A Guide to TypeScript Integration

Let's face it, dealing with errors while building your project can be frustrating, especially when it involves TypeScript. One common issue encountered is "Rollup can't resolve my typings file." This error message essentially means Rollup, a popular JavaScript module bundler, is unable to locate the necessary type definitions for your code during the build process.

Scenario:

Imagine you're building a project with Rollup and TypeScript. You've meticulously crafted your tsconfig.json file, ensuring that your code compiles correctly. However, when you run rollup -c rollup.config.js, you're met with an error message similar to:

Error: Could not resolve "my-module" from "src/main.ts"

Understanding the Issue:

Rollup relies on your configuration to determine how to handle imports and resolve dependencies. If it can't locate the necessary files, including your typings, it won't know how to correctly bundle your project. This can occur due to several factors:

• Incorrect configuration: Your rollup.config.js file might not be properly configured to include your typings files.
• Missing or misplaced typings: The TypeScript declaration files (.d.ts) might be missing or in an unexpected location.
• Module resolution issues: Rollup might not be configured to find your typings files based on your chosen module resolution strategy.

Troubleshooting and Solutions:

Here's a breakdown of how to tackle this issue:

1. Verify Your tsconfig.json:

   • Ensure that your tsconfig.json includes the outDir property, specifying the directory where your compiled JavaScript code will be placed. This directory should be included in your Rollup configuration.
   • Double-check the types property, which defines any external type definitions you're using.

2. Update your rollup.config.js:

   • Add the typescript plugin to your Rollup configuration. This plugin will handle transpiling your TypeScript code into JavaScript and ensure correct type resolution.

     import typescript from 'rollup-plugin-typescript2';
     
     export default {
         // ... other configurations
         plugins: [
             typescript({ tsconfigOverride: { compilerOptions: { outDir: 'dist' } } }),
             // ... other plugins
         ],
     };
     

   • For projects with external dependencies, consider using the resolve plugin to assist Rollup in locating the necessary files.

   import resolve from '@rollup/plugin-node-resolve';
   
   export default {
       // ... other configurations
       plugins: [
           resolve(),
           typescript({ tsconfigOverride: { compilerOptions: { outDir: 'dist' } } }),
           // ... other plugins
       ],
   };
   

3. Check for Missing Typings:

   • Ensure that all necessary type definitions for your dependencies are present in your node_modules directory.
   • If you're using third-party libraries that don't provide their own typings, consider installing @types packages from npm.

4. Adjust Module Resolution:

   • If you're using non-standard module resolution strategies (e.g., node, classic in tsconfig.json), make sure your Rollup configuration aligns with your setup.

Example:

Let's consider a simple project where we're using a custom module (my-module) with its own type definition file (my-module.d.ts):

// src/main.ts
import { myFunction } from 'my-module';

// my-module/index.js
export function myFunction(message: string): string {
  return `Hello, ${message}!`;
}

// my-module/my-module.d.ts
declare module 'my-module' {
  function myFunction(message: string): string;
}

Our Rollup configuration might look like this:

import typescript from 'rollup-plugin-typescript2';

export default {
  input: 'src/main.ts',
  output: {
    file: 'dist/main.js',
    format: 'cjs',
  },
  plugins: [
    typescript({ tsconfigOverride: { compilerOptions: { outDir: 'dist' } } }),
  ],
};

By following the steps outlined above and ensuring that your configurations are aligned, you can effectively overcome the "Rollup can't resolve my typings file" error.

Additional Tips:

• Clear and Concise: Keep your Rollup configuration and tsconfig.json files clean and organized, clearly defining your project's structure.
• Log and Debug: Use debugging tools and logging to identify any underlying issues in your setup.
• Community Support: If you encounter further issues, consider reaching out to the Rollup and TypeScript communities for assistance.

References:

• Rollup Plugin TypeScript2 Documentation
• TypeScript Compiler Options
• Rollup Node Resolve Plugin Documentation