如何声明供依赖方开发环境使用的NPM包依赖？

Hey there! Let's walk through the right way to set up dependencies for your my-library so that my-project can use your development/test helper function without any hiccups.

The Core Issue #

Your helper function relies on chai-shallow-deep-equal, but this dependency is only needed during development and testing—it has no place in production. We need to avoid cluttering production dependencies while making sure my-project has access to it when using your helper.

Recommended Solutions #

1. Use Peer Dependencies (Cleanest & Most Standard Approach)

Peer dependencies let consuming projects (like my-project) know they need to install a specific package to use certain features of your library. Here's how to configure this:

• In your my-library's package.json, add chai-shallow-deep-equal to peerDependencies, and keep it in devDependencies for your own local testing:

  {
    "peerDependencies": {
      "chai-shallow-deep-equal": "^X.Y.Z" // Use the exact version your helper requires
    },
    "peerDependenciesMeta": {
      "chai-shallow-deep-equal": {
        "optional": true
      }
    },
    "devDependencies": {
      "chai-shallow-deep-equal": "^X.Y.Z" // For testing your library locally
    }
  }
  

  • peerDependencies alerts my-project that this package is required to use your test helper.
  • peerDependenciesMeta with optional: true prevents npm from throwing an error if my-project doesn't need the helper (perfect if it's optional functionality).
  • Don't forget to document this in my-library's README:

    To use the test helper function, install chai-shallow-deep-equal as a dev dependency in your project: npm install --save-dev chai-shallow-deep-equal

2. Runtime Check with User Prompt (For Zero Friction)

If you want to guide users automatically when they try to use the helper without the dependency, add a runtime check in your helper code:

// Inside your helper function in my-library
let chaiShallowDeepEqual;
try {
  chaiShallowDeepEqual = require('chai-shallow-deep-equal');
} catch (err) {
  throw new Error(
    'Oops! To use this test helper, please install chai-shallow-deep-equal first: npm install --save-dev chai-shallow-deep-equal'
  );
}

// Proceed with your helper logic using chaiShallowDeepEqual

Pair this with the peer dependency setup above for the best user experience.

3. Bundle the Dependency (Last Resort)

If you want my-project to use the helper with zero extra steps, you can bundle chai-shallow-deep-equal into your library's build output. But note:

• This will increase the size of your library bundle.
• Only do this if the dependency is tiny and critical to the helper's functionality.

To bundle it, move chai-shallow-deep-equal to my-library's dependencies (not devDependencies) and configure your bundler (Webpack/Rollup) to include it in the final build. This is not ideal for production, though, as it adds unnecessary bloat.

Why Not Just Put It in dependencies? #

If you add chai-shallow-deep-equal to my-library's dependencies, it will be installed in my-project's production environment—even though it's only needed for testing. This adds unnecessary weight to production dependencies, which is a bad practice.

内容的提问来源于stack exchange，提问作者ChrisJ