Understanding export default in JavaScript: Example Codes

What is "export default" in JavaScript?

"export default" is a JavaScript keyword used to export a single entity (e.g., a function, object, or class) from a module for use in other modules. It's a convenient way to designate the primary or default export of a module, especially when you only want to export one item.

How does it work?

1. Placement: You place export default before the entity you want to export.
2. Naming: Unlike regular exports, you don't need to specify a name for the exported entity. The default keyword implicitly names it.
3. Import: To import the default export in another module, you simply use the module name without curly braces.

Example:

// module.js
export default function greet(name) {
  console.log(`Hello, ${name}!`);
}

// index.js
import greet from './module';

greet('Alice'); // Output: Hello, Alice!

Why use "export default"?

• Simplicity: It's a concise way to export a single entity.
• Clarity: It clearly indicates the primary export of a module.
• Common Practice: It's widely used and understood in the JavaScript community.

In the context of Node.js and ES6:

• Node.js: "export default" is essential for creating reusable modules that can be imported and used in other Node.js applications.
• ES6: This feature was introduced in ES6 (ECMAScript 2015), significantly improving module management and code organization in JavaScript.

Additional Notes:

• You can only have one default export per module.
• If you need to export multiple entities, you can use regular exports (without default) and import them using curly braces.
• While "export default" is commonly used, it's not strictly necessary. You can also use regular exports if you prefer.

Understanding export default in JavaScript: Example Codes

Example 1: Exporting a Function

// module.js
export default function greet(name) {
  console.log(`Hello, ${name}!`);
}

// index.js
import greet from './module';

greet('Alice'); // Output: Hello, Alice!

• module.js: Here, we define a function greet and export it as the default export using export default.
• index.js: We import the default export from module.js using import greet from './module';. The greet function is now available for use in index.js.

// person.js
const person = {
  name: 'John',
  age: 30
};

export default person;

// index.js
import person from './person';

console.log(person.name); // Output: John

• person.js: We create an object person and export it as the default export.
• index.js: We import the person object and can access its properties.

// car.js
class Car {
  constructor(brand) {
    this.brand = brand;
  }
}

export default Car;

// index.js
import Car from './car';

const myCar = new Car('Toyota');
console.log(myCar.brand); // Output: Toyota

• index.js: We create an instance of the Car class and can use its methods and properties.

Key Points:

• Single Default Export: A module can have only one default export.
• Import without Curly Braces: When importing the default export, you don't need to use curly braces.
• Flexibility: You can export any type of entity as the default export, including functions, objects, and classes.

• Named exports can also be used in JavaScript, allowing you to export multiple entities with specific names.
• Default exports are often used for the primary or most commonly used entity in a module.

Alternative Methods to export default in JavaScript

While export default is a popular and convenient way to export entities in JavaScript, there are other methods that can be used:

Named Exports

• Multiple Exports: You can export multiple entities with specific names.
• Import with Curly Braces: When importing named exports, you need to use curly braces to specify the names of the entities you want to import.

// module.js
export function greet(name) {
  console.log(`Hello, ${name}!`);
}

export const PI = 3.14159;

// index.js
import { greet, PI } from './module';

greet('Alice'); // Output: Hello, Alice!
console.log(PI); // Output: 3.14159

Re-exporting

• Exporting from Another Module: You can re-export entities from another module.
• Combining Exports: This is useful for creating a single module that exports entities from multiple other modules.

// module1.js
export function greet(name) {
  console.log(`Hello, ${name}!`);
}

// module2.js
export const PI = 3.14159;

// combined.js
export { greet } from './module1';
export { PI } from './module2';

// index.js
import { greet, PI } from './combined';

greet('Alice'); // Output: Hello, Alice!
console.log(PI); // Output: 3.14159

Dynamic Imports

• Lazy Loading: You can import modules dynamically based on certain conditions or user interactions.
• Improved Performance: This can improve performance, especially for large applications.

// index.js
async function loadModule() {
  const module = await import('./module');
  module.greet('Alice'); // Output: Hello, Alice!
}

loadModule();

Choosing the Right Method:

• Single Default Export: If you have only one primary entity to export, export default is a good choice.
• Multiple Named Exports: If you need to export multiple entities with specific names, named exports are suitable.
• Re-exporting: Use re-exporting to combine exports from multiple modules into a single module.
• Dynamic Imports: Consider dynamic imports for lazy loading modules, especially in large applications.