Importing values in Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the import statement in JavaScript?

The import statement is used to bring functions, objects, or values from another file or module into the current file so you can use them.

beginner

How do you import a single named value called <code>sum</code> from a module named <code>math.js</code>?

You write: <br><code>import { sum } from './math.js';</code><br>This imports only the <code>sum</code> function or value from the <code>math.js</code> file.

intermediate

What is the difference between a default import and a named import?

A default import brings in the main exported value from a module without curly braces, like <code>import myFunc from './file.js';</code>. Named imports require curly braces and import specific exported values, like <code>import { myFunc } from './file.js';</code>.

intermediate

How do you import all exported values from a module as a single object?

You use the syntax: <br><code>import * as utils from './utils.js';</code><br>This imports everything exported from <code>utils.js</code> as properties of the <code>utils</code> object.

beginner

Can you import values from a module without specifying the file extension?

In modern JavaScript environments, you usually need to include the file extension like .js when importing modules, especially in browsers. Some tools like bundlers may allow omitting it.

Which syntax correctly imports a default export named calculate from math.js?

A import calculate from './math.js';

B import { calculate } from './math.js';

C import * as calculate from './math.js';

D import './math.js';

Default exports are imported without curly braces.

How do you import only the named export multiply from math.js?

A import { multiply } from './math.js';

B import multiply from 'math.js';

C import * as multiply from './math.js';

D import multiply from './math.js';

Named exports require curly braces around the name.

What does this import statement do? import * as helpers from './helpers.js';

A Imports nothing

B Imports the default export as helpers

C Imports only the named export helpers

D Imports all exports as properties of the helpers object

The * as syntax imports all exports as an object.

Which is true about importing modules in JavaScript?

A You can import values without specifying the file path.

B You can import multiple named exports in one statement.

C You must always use curly braces for default imports.

D You cannot import from local files.

You can import multiple named exports like: import { a, b } from './file.js';

What happens if you try to import a named export that does not exist in the module?

A JavaScript throws an error at compile time.

B The import works but the value is undefined.

C JavaScript throws an error at runtime.

D The module exports all values by default.

Trying to import a non-existent named export causes a runtime error.

Explain how to import a default export and a named export from the same module.

Think about how you write import statements with and without curly braces.

Describe the difference between importing a single named export and importing all exports as an object.

Consider the use of curly braces and the * as syntax.

Practice

1. What is the correct way to import a named export calculate from a file math.js?

easy

A. import './math.js'.calculate;

B. import { calculate } from './math.js';

C. import * as calculate from './math.js';

D. import calculate from './math.js';

Solution

1. Step 1: Understand named imports syntax

   Named exports must be imported using curly braces around the exact exported name.

2. Step 2: Match syntax with example

   The syntax import { calculate } from './math.js'; correctly imports the named export calculate.

3. Final Answer:

   import { calculate } from './math.js'; -> Option B

4. Quick Check:

   Named import uses curly braces [OK]

Hint: Use curly braces for named imports, no braces for default [OK]

Common Mistakes:

• Using default import syntax for named exports
• Forgetting curly braces around named imports
• Trying to access named export as property after import

2. Which of the following is the correct syntax to import the default export from utils.js?

easy

A. import { default } from './utils.js';

B. import * as utils from './utils.js';

C. import utils from { './utils.js' };

D. import utils from './utils.js';

Solution

1. Step 1: Recall default import syntax

   Default exports are imported without curly braces using any name you choose.

2. Step 2: Identify correct syntax

   import utils from './utils.js'; correctly imports the default export.

3. Final Answer:

   import utils from './utils.js'; -> Option D

4. Quick Check:

   Default import no braces [OK]

Hint: Default imports have no braces, named imports do [OK]

Common Mistakes:

• Using curly braces for default import
• Incorrect braces placement
• Using * as for default import

3. Given export const name = 'Alice'; in person.js, what will be the output of this code?

import { name } from './person.js';
console.log(name);

medium

A. Alice

B. ReferenceError

C. undefined

D. null

Solution

1. Step 1: Understand named export and import

   The variable name is exported as a named export and imported correctly with curly braces.

2. Step 2: Check the logged value

   Since name is 'Alice', console.log(name); outputs 'Alice'.

3. Final Answer:

   Alice -> Option A

4. Quick Check:

   Named import logs exported value [OK]

Hint: Named import logs exported value directly [OK]

Common Mistakes:

• Forgetting curly braces causing ReferenceError
• Expecting default import without braces
• Confusing undefined with missing import

4. What is wrong with this import statement?

import { sum } from './math.js'
console.log(sum(2, 3));

Assuming sum is a default export in math.js.

medium

A. Missing semicolon after import

B. Wrong file path

C. Using curly braces for default export import

D. sum is not a function

Solution

1. Step 1: Identify export type

   The problem states sum is a default export, so it should be imported without curly braces.

2. Step 2: Check import syntax

   Using curly braces imports named exports, so import { sum } is incorrect for default export.

3. Final Answer:

   Using curly braces for default export import -> Option C

4. Quick Check:

   Default export no braces [OK]

Hint: Default export imports never use braces [OK]

Common Mistakes:

• Confusing default and named imports
• Ignoring export type in import
• Assuming semicolon is mandatory for correctness

5. You have two files:

// colors.js
export const red = '#FF0000';
export const blue = '#0000FF';
export default 'colors';

// app.js
import colors, { red, green } from './colors.js';
console.log(colors, red, green);

What will happen when running app.js?

hard

A. SyntaxError due to invalid import

B. Logs: colors #FF0000 undefined

C. Logs: undefined #FF0000 undefined

D. ReferenceError: green is not defined

Solution

1. Step 1: Analyze exports in colors.js

   There is a default export 'colors' and named exports 'red' and 'blue'. No 'green' export exists.

2. Step 2: Analyze import statement in app.js

   It imports default as colors and named red, but green does not exist, causing a SyntaxError during module loading.

3. Final Answer:

   SyntaxError due to invalid import -> Option A

4. Quick Check:

   Missing named export causes import error [OK]

Hint: Missing named exports cause import errors [OK]

Common Mistakes:

• Thinking missing named import becomes undefined
• Confusing default and named imports
• Expecting ReferenceError at runtime