yarn ts-node-dev requires defining dependency to src folder

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02-09-2024

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Understanding "yarn ts-node-dev requires defining dependency to src folder" Error

This article will delve into a common problem encountered when using ts-node-dev for development and TypeScript projects. We'll analyze the reasons behind the error "Your application tried to access src, but it isn't declared in your dependencies," along with solutions and best practices.

The Problem

As outlined in the Stack Overflow question by user12345678, the setup involves:

• Project Structure: A standard structure with a src folder for source files and a dist folder for compiled output.
• Development: Using ts-node-dev to run TypeScript code directly.
• Production: Using tsc to compile the code and then running the compiled JavaScript.

The error arises when running yarn ts-node-dev or yarn start with ts-node, as the runtime cannot find the src folder, even though tsc successfully compiles it.

Why does this happen?

This error occurs due to how Node.js manages dependencies and module resolution. When running code with ts-node-dev or ts-node, Node.js attempts to resolve modules based on the node_modules directory and its internal module resolution algorithm.

In this case, the src folder is not part of the node_modules tree, and it's not explicitly listed as a dependency in the package.json. Hence, Node.js cannot locate the necessary files within the src folder.

Solutions

1. Explicit Dependency:

   The recommended solution, as mentioned by user12345678, is to add the src folder as a dependency in the package.json file:

   {
     "name": "test-app",
     "packageManager": "[email protected]",
     "version": "0.1.0",
     "description": "test-app",
     "scripts": {
       "dev": "ts-node-dev --exit-child ./src/index.ts",
       "start": "ts-node ./src/index.ts",
       "build": "tsc"
     },
     "devDependencies": {
       "@tsconfig/node-lts": "^20.1.3",
       "@types/express": "^4",
       "@types/node": "^20.12.7",
       "ts-node": "^10.9.2",
       "ts-node-dev": "^2.0.0",
       "typescript": "^5.4.5"
     },
     "dependencies": {
       "express": "^4.19.2",
       "graphql": "^16.8.1",
       "graphql-http": "^1.22.1",
       "src": "." // Adding src as a dependency
     }
   }
   

   This approach makes the src folder directly accessible to the Node.js runtime. However, it might feel unnatural to include your source code directory as a dependency.

2. Using tsconfig.json

   You can configure tsconfig.json to explicitly include the src folder in the compilation process. This approach allows for a cleaner package.json without directly adding the src folder as a dependency. Here's a modified tsconfig.json:

   {
     "extends": "@tsconfig/node-lts/tsconfig.json",
     "include": ["src/**/*.ts"], // Specify files to include
     "compilerOptions": {
       /* Emit */
       "outDir": "dist"
     }
   }
   

   By specifying src/**/*.ts, you explicitly inform TypeScript which files should be included for compilation, eliminating the need to declare the src folder as a dependency in package.json.

Additional Considerations

• Best Practices: Consider using a build tool like webpack or parcel for managing dependencies and bundling your application for both development and production environments. These tools offer sophisticated features like module resolution, transpilation, and optimization.
• Module Resolution: To avoid potential issues, ensure that you are using relative paths within your code to import modules correctly. For instance, in your src/server.ts file, you should use relative paths like import { MyComponent } from './components/MyComponent';

Conclusion

The "yarn ts-node-dev requires defining dependency to src folder" error stems from Node.js's module resolution mechanism. While explicitly adding src to package.json is a functional solution, configuring tsconfig.json is a cleaner alternative. Ultimately, a more robust approach involves using a build tool for managing dependencies and building your project for various environments. This provides a more structured and efficient development workflow, enhancing code maintainability and reducing the likelihood of encountering such errors.