When developing with TypeScript, how to solve the problem of module parsing and declaration file merging of math packages in projects created by pnpm?

TypeScript: Module parsing and declaration files of math package in pnpm project conflict

This article discusses how to resolve the problem of module parsing and declaration file merging of math packages in TypeScript projects using pnpm, especially when extending the type declaration of math packages.

Problem scenario

In a project created with pnpm, we successfully introduced math package and used it normally. However, when we try to extend math package's divide function type declaration and create the math-extensions.d.ts file, a module overwrite problem occurs, resulting in a VS Code error.

Questions and Answers

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

declare module is indeed intended to merge declarations, but the problem is the order and priority of the declaration files loading by the TypeScript compiler. If the loading priority of math-extensions.d.ts is higher than the declaration file provided by math package, overwrite will occur, resulting in an error.

Question 2: Why does math-extensions.d.ts take effect when using non-relative import?

Although non-relative imports preferentially look up node_modules , the TypeScript compiler also looks up declaration files in the project based on baseUrl and include configurations in tsconfig.json . If math-extensions.d.ts is located in the directory specified by include and baseUrl is the project root directory, it will be loaded.

Solution

The solution is mainly focused on avoiding declaration file conflicts and controlling the loading order:

1. Rename or adjust the location of the declaration file: Rename the math-extensions.d.ts file, or move it to a directory that does not conflict with the math package declaration file, for example, create a types directory specifically to store custom type declarations.

2. Configure paths of tsconfig.json : Through paths configuration, explicitly specify the parsing path of the math module, and priority is given to loading the declaration file in node_modules . For example:

    {
     "compilerOptions": {
       "outDir": "dist",
       "baseUrl": ".",
       "moduleResolution": "node",
       "paths": {
         "math": ["node_modules/math"]
       }
     },
     "include": ["src/**/*"]
   }

   This configuration ensures that the TypeScript compiler prefers to load its declaration files from the node_modules directory when parsing math modules, and avoids overwriting by math-extensions.d.ts .

Through the above methods, the TypeScript module parsing and declaration file merging problems can be effectively solved to ensure the smooth compilation and operation of the project. Remember, a clear project structure and a reasonable tsconfig.json configuration are the key to avoiding such problems.

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