How to resolve the TypeScript module parsing and declaration file merging issues when the math package created using pnpm is introduced in the example package?

Detailed explanation and solution for conflicts between TypeScript module parsing and declaration files

This article discusses how to resolve the conflict between the custom declaration file and the installed package declaration file in the TypeScript project managed using pnpm. Suppose we have a package called math and use it in the example project. When trying to extend the divide function type of math package, creating the math-extensions.d.ts declaration file in example project results in a module overwrite error.

Problem description

The divide function is defined in the math package, and the example project is successfully introduced and used. Then, in the example project, create the math-extensions.d.ts file and try to extend the divide function type, but it causes VSCode to report an error, prompting a module conflict.

Questions and Answers

Question 1: Shouldn’t declare module merge statements? Why does VSCode report an error?

declare module is indeed used for merge statements, but the reason for the error may be related to the following factors:

1. Declaration file path and priority: The order in which TypeScript looks for declaration files will affect the final result. If multiple declaration files exist, TypeScript will select one of them based on path priority, causing the other declaration files to be ignored or conflicted.
2. tsconfig.json configuration: baseUrl and moduleResolution configurations will affect the path of TypeScript to find modules. Incorrect configuration may cause TypeScript to not find the correct declaration file or find the wrong declaration file.
3. VSCode real-time type checking: VSCode performs type checking when editing, which may detect conflicts earlier than the TypeScript compiler, thus prompting errors.

Question 2: Shouldn't non-relative imports only look for node_modules ? Why does math-extensions.d.ts take effect?

Non-relative imports usually give priority to looking for node_modules , but TypeScript's module parsing rules are adjusted according to tsconfig.json configuration:

1. The impact of baseUrl : If baseUrl is set to . (project root directory), TypeScript will start looking from the project root directory, and math-extensions.d.ts is naturally within the search range.
2. Path priority: The path of math-extensions.d.ts may have higher priority than the declaration file in node_modules , causing it to be parsed first.
3. Declaration file merge failed: Even if math-extensions.d.ts is in effect, it will cause an error if it conflicts with math package's declaration.

Solution

The best way to solve this problem is to avoid creating a declaration file with the same name as the installed package in example project. The following options are available:

1. Add an extension in the math package: Move the math-extensions.d.ts file into the math package and publish as part of it. This ensures that the extension is always consistent with the original package's declaration.
2. Use types fields: Add the types field in package.json of the math package and point to its type declaration file. This ensures that TypeScript correctly finds and uses the type declaration of math package.
3. Use environment variables to distinguish: use an extra declaration file in the development environment and remove it at build time. This requires a more complex build process.
4. More accurate tsconfig.json configuration: By adjusting baseUrl , paths and other configurations, make sure TypeScript prioritizes finding declaration files in node_modules and avoids conflicts with local declaration files.

Through the above analysis and solutions, we can effectively solve the problem of TypeScript module parsing and declaration file merging, and improve the maintainability and reliability of the code. Which option to choose depends on the specific situation and complexity of the project. Prioritize adding extensions to the source package or using types fields, which is usually a cleaner and easier to maintain.

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