Default exports in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a default export in JavaScript modules?

A default export is a way to export a single value or entity from a module so that it can be imported without using curly braces. It represents the main exported value of the module.

beginner

How do you write a default export for a function named greet?

You write: <pre>export default function greet() {<br>  console.log('Hello!');<br>}</pre> This exports the <code>greet</code> function as the default export.

beginner

How do you import a default export from a module named <code>math.js</code>?

You write: <pre>import anyName from './math.js';</pre> You can choose any name for the imported value because it is the default export.

beginner

Can a module have more than one default export?

No, a module can only have one default export. Trying to export more than one default will cause an error.

intermediate

What is the difference between default export and named export?

Default export exports a single main value without curly braces when importing. Named exports export multiple values and require curly braces when importing.

How do you import a default export from a module?

A import { value } from 'module';

B require('module').value;

C import * as value from 'module';

D import value from 'module';

Default exports are imported without curly braces using: import value from 'module';

Which of the following is a correct way to export a default value?

A export 42 as default;

B export { default: 42 };

C export default 42;

D export default = 42;

You export a default value simply by writing: export default 42;

Can a module have multiple default exports?

A No, only one default export is allowed.

B Yes, but only two.

C No, default exports are not allowed.

D Yes, unlimited default exports.

A module can only have one default export.

What happens if you import a default export with a different name?

A It causes an error.

B It works fine; you can rename default imports.

C It imports nothing.

D It imports all named exports.

Default exports can be imported with any name you choose.

Which syntax imports both default and named exports from a module?

A import defaultExport, { namedExport } from 'module';

B import { defaultExport, namedExport } from 'module';

C import * as all from 'module';

D import defaultExport from 'module';

You import default and named exports together like this: import defaultExport, { namedExport } from 'module';

Explain what a default export is and how it differs from named exports.

Think about how you import the main thing from a module.

Describe how to export and import a default function from a JavaScript module.

Focus on the function keyword and import naming.

Practice

1. What is a default export in JavaScript modules?

easy

A. A single main value or function exported from a file without curly braces when importing.

B. Multiple named values exported from a file using curly braces when importing.

C. A way to export variables only, not functions.

D. A special export that requires double curly braces when importing.

Solution

1. Step 1: Understand export types

   JavaScript modules can export multiple named items or one default item.

2. Step 2: Identify default export usage

   Default export is a single main export imported without curly braces.

3. Final Answer:

   A single main value or function exported from a file without curly braces when importing. -> Option A

4. Quick Check:

   Default export = single main export without braces [OK]

Hint: Default exports import without braces, named exports need braces [OK]

Common Mistakes:

• Confusing default export with named exports
• Using curly braces when importing default export
• Thinking default export can export multiple items

2. Which of the following is the correct syntax to export a default function named greet?

easy

A. default export function greet() {}

B. export function default greet() {}

C. export default function greet() {}

D. export greet default function() {}

Solution

1. Step 1: Recall default export syntax

   The correct syntax is to write export default followed by the function declaration.

2. Step 2: Check each option

   Only export default function greet() {} matches the correct syntax: export default function greet() {}.

3. Final Answer:

   export default function greet() {} -> Option C

4. Quick Check:

   export default + function name = correct syntax [OK]

Hint: Remember: 'export default' comes before function name [OK]

Common Mistakes:

• Placing 'default' after function name
• Using 'default export' instead of 'export default'
• Mixing order of keywords

3. Given the file math.js with content:

export default function add(a, b) { return a + b; }

What will be the output of this code?

import add from './math.js';
console.log(add(3, 4));

medium

A. undefined

B. 7

C. TypeError

D. NaN

Solution

1. Step 1: Understand import of default export

   The function add is exported as default and imported without braces correctly.

2. Step 2: Evaluate function call

   Calling add(3, 4) returns 3 + 4 = 7, which is logged.

3. Final Answer:

   7 -> Option B

4. Quick Check:

   Default import calls function correctly = 7 [OK]

Hint: Default export imports as named variable, call normally [OK]

Common Mistakes:

• Using curly braces when importing default export
• Expecting undefined because of wrong import
• Confusing default export with named export

4. Identify the error in this code snippet:

import { greet } from './hello.js';
export default function greet() { return 'Hi'; }

medium

A. Cannot import default export using curly braces.

B. Function cannot be named greet when exported default.

C. Missing semicolon after export statement.

D. Default export must be a variable, not a function.

Solution

1. Step 1: Check import syntax

   Importing default export must be done without curly braces, but here curly braces are used.

2. Step 2: Confirm export syntax

   Exporting default function named greet is valid, so no error there.

3. Final Answer:

   Cannot import default export using curly braces. -> Option A

4. Quick Check:

   Default import no braces, braces cause error [OK]

Hint: Default exports import without braces; braces mean named import [OK]

Common Mistakes:

• Using curly braces to import default export
• Thinking default export must be unnamed
• Assuming semicolon is mandatory for export

5. You have two files:

// file1.js
const value = 42;
export default value;

// file2.js
import val from './file1.js';
console.log(val);

How can you change file1.js to export both value as default and a named constant name with value 'Answer'?

hard

A. Cannot export default and named exports together in one file.

B. Change default export to named export for value and export name as default.

C. Use export default { value, name }; to export both.

D. Add export const name = 'Answer'; alongside default export.

Solution

1. Step 1: Understand export combinations

   JavaScript allows one default export and multiple named exports in the same file.

2. Step 2: Add named export alongside default

   Adding export const name = 'Answer'; exports a named constant while keeping default export.

3. Final Answer:

   Add export const name = 'Answer'; alongside default export. -> Option D

4. Quick Check:

   Default + named exports can coexist [OK]

Hint: Default export plus named exports can be in same file [OK]

Common Mistakes:

• Thinking default and named exports cannot coexist
• Trying to export multiple defaults
• Using object as default export to hold multiple values