JavaScript Modules: Understanding Default Exports
Quick Answer
Default exports in JavaScript modules allow you to export a single value or entity from a module, making it the primary exported item. This simplifies importing by enabling you to import without curly braces and rename the import easily.
Learning Objectives
- Explain the purpose of Default Exports in a practical learning context.
- Identify the main ideas, terms, and decisions involved in Default Exports.
- Apply Default Exports in a simple real-world scenario or practice task.
Introduction to Default Exports in JavaScript Modules
JavaScript modules help organize code by encapsulating functionality into reusable files. One key feature is the ability to export and import code between modules.
Default exports allow a module to export a single main value or function, making it straightforward to import and use in other parts of your application.
Default exports provide a clean and simple way to export the primary value from a module.
What Are Default Exports?
A default export is a way to export a single value, object, or function from a module. Unlike named exports, a module can only have one default export.
This export is considered the 'main' exported value of the module.
- Only one default export allowed per module.
- Can export functions, classes, objects, primitives, or expressions.
- Simplifies import syntax by omitting curly braces.
Syntax of Default Exports
There are two common ways to declare a default export in a module: inline and separate export statements.
- Inline default export: `export default function() {}` or `export default class {}`.
- Separate default export: declare a variable or function, then export it as default using `export default variableName;`.
Example of Inline Default Export
You can export a function directly as the default export.
Example of Separate Default Export
Declare a constant or function first, then export it as default.
Importing Default Exports
When importing a default export, you do not use curly braces. You can also rename the import to any identifier you prefer.
This flexibility makes default exports convenient for modules that export a single main feature.
- Import syntax: `import anyName from './module.js';`
- No curly braces needed for default imports.
- You can rename the imported value freely.
When to Use Default Exports
Default exports are ideal when your module exports a single main entity, such as a class, function, or object.
They help keep import statements clean and intuitive.
- Export a single main component or utility.
- Simplify imports in consuming modules.
- Improve code readability by emphasizing the primary export.
Practical Example
This module exports a function named 'greet' as the default export.
Here, the constant PI is exported as the default export of the module.
This imports the default export from 'greetModule.js' and calls it.
Examples
export default function greet() {
console.log('Hello from default export!');
}This module exports a function named 'greet' as the default export.
const PI = 3.14159;
export default PI;Here, the constant PI is exported as the default export of the module.
import greet from './greetModule.js';
greet();This imports the default export from 'greetModule.js' and calls it.
Best Practices
- Use default exports for modules that export a single main value or function.
- Keep default export names meaningful to improve code readability.
- Avoid mixing default and named exports excessively in the same module to reduce confusion.
- Use consistent naming conventions when importing default exports.
Common Mistakes
- Trying to have multiple default exports in one module (not allowed).
- Using curly braces when importing default exports.
- Confusing default exports with named exports syntax.
- Renaming default imports to unclear or inconsistent names.
Hands-on Exercise
Create a Module with Default Export
Write a JavaScript module that exports a default function which returns a greeting message.
Expected output: A module file exporting a default function.
Hint: Use `export default function` syntax.
Import and Use a Default Export
Import the default export from the module you created and call the function to display the greeting.
Expected output: Greeting message printed to the console.
Hint: Use `import name from './module.js'` syntax without curly braces.
Interview Questions
What is the difference between default exports and named exports in JavaScript modules?
InterviewDefault exports allow a module to export a single main value without requiring curly braces during import, while named exports allow exporting multiple values that must be imported using their exact names inside curly braces.
Can a module have more than one default export?
InterviewNo, a module can only have one default export.
What is Default Exports, and why is it useful?
BeginnerDefault exports in JavaScript modules allow you to export a single value or entity from a module, making it the primary exported item.
MCQ Quiz
1. What is the best first step when learning Default Exports?
A. Understand the purpose and basic idea
B. Skip directly to advanced implementation
C. Ignore examples and practice
D. Memorize terms without context
Correct answer: A
Starting with the purpose and basic idea makes later examples and practice easier to understand.
2. Which activity helps reinforce Default Exports?
A. Reading once without practice
B. Building or writing a small practical example
C. Avoiding review questions
D. Skipping the summary
Correct answer: B
A small practical example helps connect the topic to real usage.
3. Which statement is most accurate about this topic?
A. Default exports in JavaScript modules allow you to export a single value or entity from a module, making it the primary exported item.
B. Default Exports never needs examples
C. Default Exports is unrelated to practical work
D. Default Exports should be learned without checking results
Correct answer: A
The correct option is based on the available topic explanation.
Key Takeaways
- Default exports in JavaScript modules allow you to export a single value or entity from a module, making it the primary exported item.
- This simplifies importing by enabling you to import without curly braces and rename the import easily.
- JavaScript modules help organize code by encapsulating functionality into reusable files.
- One key feature is the ability to export and import code between modules.
- Default exports allow a module to export a single main value or function, making it straightforward to import and use in other parts of your application.
Summary
Default exports in JavaScript modules provide a simple way to export a single main value or function from a module.
They simplify import statements by allowing you to import without curly braces and rename the import freely.
Using default exports appropriately improves code clarity and maintainability in modular JavaScript applications.
Frequently Asked Questions
Can I have both default and named exports in the same module?
Yes, a module can have one default export and multiple named exports simultaneously.
How do I import a default export with a different name?
You can rename a default import by specifying any identifier you want, for example: `import myFunc from './module.js';`.
What happens if I use curly braces when importing a default export?
Using curly braces when importing a default export will cause a syntax error or undefined import because default exports are imported without curly braces.
