What is the difference between export and export default?

In JavaScript, particularly when using ES6 modules, understanding the distinction between export and export default is crucial for effective module management and code organization. Both are used to export functions, objects, or primitives from a module, but they serve different purposes and have different syntactical requirements. Below, I will elaborate on these differences, provide practical examples, and highlight best practices and common mistakes.

Understanding export

The export statement is used to export multiple named exports from a module. This allows you to export several variables, functions, or classes from a single module, which can then be imported by other modules using their respective names.

Example of Named Exports

 // math.js
export const PI = 3.14;
export function add(x, y) {
    return x + y;
}
export class Calculator {
    static multiply(x, y) {
        return x * y;
    }
}

In the above example, we have a module named math.js that exports a constant, a function, and a class. Each of these exports can be imported individually in another module.

Importing Named Exports

 // app.js
import { PI, add, Calculator } from './math.js';

console.log(PI); // 3.14
console.log(add(2, 3)); // 5
console.log(Calculator.multiply(2, 3)); // 6

When importing named exports, you must use the exact names as they were exported, enclosed in curly braces. This ensures clarity and prevents naming conflicts.

Understanding export default

On the other hand, export default is used to export a single value or object from a module. This is particularly useful when a module is designed to export one primary functionality or object, making it easier to import without needing to remember specific names.

Example of Default Export

 // calculator.js
export default class Calculator {
    static multiply(x, y) {
        return x * y;
    }
}

In this example, we have a module calculator.js that exports a single class as the default export. This class can be imported without using curly braces.

Importing Default Exports

 // app.js
import Calculator from './calculator.js';

console.log(Calculator.multiply(2, 3)); // 6

When importing a default export, you can choose any name for the imported value. This flexibility allows for cleaner and more intuitive code, especially when the module's purpose is clear.

Best Practices

• Use named exports for multiple exports: If your module contains multiple functions or variables that can be logically grouped, use named exports to enhance clarity.
• Use default exports for single exports: When a module is designed to export a single entity, prefer default exports for simplicity.
• Maintain consistency: Stick to a consistent approach within your project. If you use named exports in one module, try to do the same in others unless there’s a compelling reason to diverge.
• Document your exports: Clearly document what each export does, especially in larger projects, to help other developers understand the module's purpose quickly.

Common Mistakes

• Confusing named and default exports: A common mistake is trying to import a default export using curly braces, which will result in an error. Always remember that default exports do not require braces.
• Mixing named and default exports: While it’s possible to mix both types in a single module, it can lead to confusion. If you do mix them, ensure that your import statements are clear and unambiguous.
• Not using the correct file extensions: When importing modules, always ensure that you include the correct file extension (e.g., .js) to avoid runtime errors.

In conclusion, understanding the differences between export and export default is essential for effective module management in JavaScript. By following best practices and avoiding common mistakes, developers can create more maintainable and understandable codebases.