Exporting values in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of exporting values in JavaScript modules?

Exporting values allows you to share variables, functions, or objects from one file so other files can use them.

beginner

How do you export a single value as the default export in JavaScript?

Use export default followed by the value, for example: export default function() {}.

intermediate

What is the difference between named exports and default exports?

Named exports let you export multiple values by name, while default export lets you export one main value per module.

beginner

How do you export multiple values from a module?

You list them inside curly braces after the export keyword, like export { a, b, c }.

beginner

Can you export a value immediately when declaring it? Give an example.

Yes, for example: <code>export const pi = 3.14;</code> exports the constant <code>pi</code> right away.

Which keyword is used to export a value from a JavaScript module?

A import

B require

C module

D export

The export keyword is used to share values from a module.

How do you export a function as the default export?

A export default function myFunc() {}

B export function myFunc() {}

C export { myFunc }

D default export function myFunc() {}

Use export default function myFunc() {} to export a function as default.

Which syntax exports multiple named values at once?

A export default { a, b }

B export (a, b)

C export { a, b }

D export a, b

Use export { a, b } to export multiple named values.

Can a module have more than one default export?

A No, only one default export

B Yes, but only two

C Yes, unlimited

D Only if named

A module can have only one default export.

What does this code do? export const name = 'Alice';

A Imports a constant named name

B Exports a constant named name

C Declares a variable without exporting

D Exports a default value

It exports a constant named name with the value 'Alice'.

Explain how to export multiple values from a JavaScript module and how to import them.

Think about curly braces and matching names.

Describe the difference between default export and named export with examples.

One uses 'export default', the other uses 'export { }'.

Practice

1. What does the export keyword do in JavaScript modules?

easy

A. It makes variables or functions available to other files.

B. It imports code from other files.

C. It runs the code immediately.

D. It deletes variables after use.

Solution

1. Step 1: Understand the purpose of export

   The export keyword is used to share variables or functions from one file so other files can use them.

2. Step 2: Differentiate from import and execution

   import brings code in, and running code is separate; export only shares code.

3. Final Answer:

   It makes variables or functions available to other files. -> Option A

4. Quick Check:

   export shares code = A [OK]

Hint: Export means share code to other files [OK]

Common Mistakes:

• Confusing export with import
• Thinking export runs code
• Believing export deletes variables

2. Which of the following is the correct syntax to export a constant named PI?

easy

A. const PI = 3.14; export PI;

B. export const PI = 3.14;

C. export = const PI = 3.14;

D. const PI = 3.14 export;

Solution

1. Step 1: Check correct export syntax

   To export a variable while declaring it, use export const PI = 3.14;.

2. Step 2: Identify syntax errors in other options

   const PI = 3.14; export PI; (const PI = 3.14; export PI;) uses incorrect export syntax after declaration (needs export { PI };); B and D have invalid syntax.

3. Final Answer:

   export const PI = 3.14; -> Option B

4. Quick Check:

   export const PI = 3.14; = C [OK]

Hint: Put export before variable or function declaration [OK]

Common Mistakes:

• Placing export after variable declaration
• Using incorrect export assignment syntax
• Missing semicolons causing confusion

3. Given this code in math.js:

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

export const number = 5;

What will be the output of this code in app.js?

import { add, number } from './math.js';
console.log(add(number, 10));

medium

A. 15

B. 510

C. NaN

D. SyntaxError

Solution

1. Step 1: Understand imported values

   The function add adds two numbers, and number is 5.

2. Step 2: Calculate the function call

   Calling add(5, 10) returns 15.

3. Final Answer:

   15 -> Option A

4. Quick Check:

   5 + 10 = 15 [OK]

Hint: Add imported values as normal functions [OK]

Common Mistakes:

• Treating number as string causing concatenation
• Forgetting to import both values
• Syntax errors from wrong import path

4. What is wrong with this code in utils.js?

function greet() {
  return 'Hello';
}

export greet;

medium

A. Missing export keyword before function declaration

B. No error; code is correct

C. Incorrect export syntax; should be export { greet };

D. Function greet cannot be exported

Solution

1. Step 1: Identify export syntax error

   The line export greet; is invalid syntax in JavaScript modules.

2. Step 2: Correct export syntax for existing functions

   To export an already declared function, use export { greet };.

3. Final Answer:

   Incorrect export syntax; should be export { greet }; -> Option C

4. Quick Check:

   Export existing function with braces = D [OK]

Hint: Use export { name } for existing declarations [OK]

Common Mistakes:

• Trying to export without braces
• Confusing export declaration with export statement
• Assuming export greet; is valid

5. You want to export multiple values from a file: a function calculate, a constant PI, and a variable radius. Which is the best way to export all three at once?

hard

A. export calculate, PI, radius;

B. export default calculate, PI, radius;

C. export const calculate, PI, radius;

D. export { calculate, PI, radius };

Solution

1. Step 1: Understand exporting multiple named values

   To export several named values together, use export { name1, name2, name3 };.

2. Step 2: Eliminate incorrect syntax options

   Options A, C, and D are invalid syntax; A lacks braces, C misuses export const for multiple, D is for default export only.

3. Final Answer:

   export { calculate, PI, radius }; -> Option D

4. Quick Check:

   Use braces to export multiple names = B [OK]

Hint: Use export { a, b, c } to export many values [OK]

Common Mistakes:

• Trying to export multiple values without braces
• Using export default for multiple named exports
• Mixing const and export syntax incorrectly