JavaScript ES6 Modules: `import` and `export` Syntax

Table of Contents

1. Fundamental Concepts
2. Export Syntax
   • Named Exports
   • Default Exports
3. Import Syntax
   • Importing Named Exports
   • Importing Default Exports
   • Combined Imports
4. Common Practices
   • Module Organization
   • Using Aliases
5. Best Practices
   • Keep Modules Small and Focused
   • Use Named Exports for Multiple Exports
6. Conclusion
7. References

Fundamental Concepts

In JavaScript, a module is simply a file. Each module has its own scope, which means that variables, functions, and classes defined in one module are not accessible in other modules by default. The export keyword is used to make variables, functions, or classes available outside of the module, and the import keyword is used to bring those exported items into another module.

Export Syntax

Named Exports

Named exports allow you to export multiple values from a module. You can export variables, functions, or classes by specifying their names.

// math.js
export const add = (a, b) => a + b;
export const subtract = (a, b) => a - b;

Default Exports

A module can have one default export. The default export is useful when a module only has one main thing to export.

// greeting.js
const greeting = () => {
    return 'Hello, World!';
};
export default greeting;

Import Syntax

Importing Named Exports

To import named exports, you need to specify the names of the exports inside curly braces.

// main.js
import { add, subtract } from './math.js';

console.log(add(5, 3)); // Output: 8
console.log(subtract(5, 3)); // Output: 2

Importing Default Exports

When importing a default export, you don’t need to use curly braces. You can give the imported item any name you like.

// main.js
import greeting from './greeting.js';

console.log(greeting()); // Output: Hello, World!

Combined Imports

You can combine named and default imports in a single import statement.

// main.js
import defaultExport, { add, subtract } from './math.js';

Common Practices

Module Organization

It’s a good practice to organize your modules based on their functionality. For example, you can have separate modules for handling data, UI components, and utility functions.

Using Aliases

You can use aliases when importing named exports to avoid naming conflicts.

// main.js
import { add as addition, subtract as subtraction } from './math.js';

console.log(addition(5, 3)); // Output: 8
console.log(subtraction(5, 3)); // Output: 2

Best Practices

Keep Modules Small and Focused

Each module should have a single responsibility. This makes the code easier to understand, test, and maintain.

Use Named Exports for Multiple Exports

If a module has multiple things to export, use named exports instead of default exports. This makes it clear what is being exported and imported.

Conclusion

JavaScript ES6 modules with the import and export syntax provide a powerful way to organize and share code. By understanding the fundamental concepts, different export and import syntaxes, and following common and best practices, you can write more modular, maintainable, and reusable JavaScript code.

References

• MDN Web Docs - JavaScript modules
• ECMAScript 6 Modules: The Definitive Guide