如何从npm模块myLib的index.js引用ES6类并创建实例？

Hey, let's troubleshoot that import error you're seeing. The vast majority of the time, this comes down to a mismatch between how you export your class in mod1.js and how you try to import it in index.js. Let's walk through the most common scenarios:

1. If you're using a default export in mod1.js #

If your class is the primary export from mod1.js, use a default export:

// myLib/mod1.js
export default class MyAwesomeClass {
  constructor() {
    // Your class logic here
    console.log("Instance created!");
  }
}

To import this in index.js, you don't need curly braces—just import the class directly (you can even rename it if you want):

// index.js
// Import with the original name
import MyAwesomeClass from 'myLib/mod1';
// Or rename it for convenience
import CustomName from 'myLib/mod1';

// Create your instance
const myInstance = new MyAwesomeClass();
// Or using the renamed import
const anotherInstance = new CustomName();

2. If you're using a named export in mod1.js #

If you're exporting multiple items from mod1.js (or prefer explicit named exports), use this pattern:

// myLib/mod1.js
export class MyAwesomeClass {
  constructor() {
    console.log("Instance created!");
  }
}

// You might have other exports too, like:
export const someUtilityFunction = () => { /* ... */ };

When importing, wrap the class name in curly braces to match the export:

// index.js
import { MyAwesomeClass } from 'myLib/mod1';

// Create your instance
const myInstance = new MyAwesomeClass();

// If you want to rename the imported class:
import { MyAwesomeClass as CustomName } from 'myLib/mod1';
const renamedInstance = new CustomName();

3. Handling CommonJS exports (if myLib uses CommonJS instead of ES6) #

Some older npm packages use CommonJS syntax (module.exports) instead of ES6 exports. Adapt your import like this:

• If mod1.js exports the class directly:

  // myLib/mod1.js (CommonJS)
  class MyAwesomeClass { /* ... */ }
  module.exports = MyAwesomeClass;
  

  Import it like a default ES6 export:

  // index.js
  import MyAwesomeClass from 'myLib/mod1';
  const instance = new MyAwesomeClass();
  

• If mod1.js exports an object containing the class:

  // myLib/mod1.js (CommonJS)
  class MyAwesomeClass { /* ... */ }
  module.exports = { MyAwesomeClass };
  

  Use named import syntax:

  // index.js
  import { MyAwesomeClass } from 'myLib/mod1';
  const instance = new MyAwesomeClass();
  

Quick Check: Ensure Your Project is Configured for ES Modules #

If you're running this in Node.js, add the "type": "module" field to your package.json—this tells Node.js to treat .js files as ES modules instead of CommonJS:

{
  "name": "your-project",
  "type": "module",
  // ... other project fields
}

Double-check that your export and import syntax match, and you should be able to create instances of your class without errors!

内容的提问来源于stack exchange，提问作者The Nomad