"Import vs. Export: The Ultimate Face-off in the Package.json

1. Import Field:

Purpose: Defines the entry point specifically for ESM modules, typically used in modern Node.js or ESM-only packages.
Use Case: Provides a single, straightforward entry for the import syntax. It’s ideal when your package only needs to support ESM and doesn't require CommonJS.
Example:

  {
    "import": "./esm/index.js"
  }

Introduced In: Node.js 16+.
Flexibility: Simple and only focuses on ESM.
When to Use: For clean, ESM-only packages that don't need support for other formats.

2. Exports Field:

Purpose: Provides fine-grained control over what parts of your package are exposed, supporting both ESM and CommonJS.
Use Case: Allows you to define multiple entry points or formats, such as specifying different paths for import (ESM) and require (CommonJS).
Example:

  {
    "exports": {
      ".": {
        "import": "./esm/index.js",
        "require": "./cjs/index.js"
      },
      "./feature": {
        "import": "./esm/feature.js",
        "require": "./cjs/feature.js"
      }
    }
  }

Introduced In: Node.js 12+.
Flexibility: Highly flexible, allowing you to manage different module systems and entry points.
When to Use: Ideal for packages that need to support both CommonJS and ESM or have different entry points for different use cases.

Key Differences:

Criteria	Import Field	Exports Field
Purpose	Single entry for ESM	Multiple entry points for ESM & CommonJS
Introduced In	Node.js 16+	Node.js 12+
Use Case	For ESM-only packages	For packages supporting both formats
Flexibility	Simple, one entry point	Highly flexible, multiple formats
Format Compatibility	ESM only	Both ESM and CommonJS
Example	`import` points to one ESM file	`exports` can define paths for multiple formats and files
When to Use	When you only need ESM	When you need to handle multiple formats and entry points
Configuration	Simple	Complex but more powerful
Precedence	Used if `exports` is absent	Takes precedence over `import`
Complexity	Low	Higher, supports multiple conditions

Summary:

Use import when you want a straightforward entry for ESM.
Use exports when you need more control, allowing for multiple entry points and formats, supporting both ESM and CommonJS.

Both fields allow you to tailor how your package is imported, but exports offers far more versatility for more complex scenarios.