Why Importing values in Javascript? - Purpose & Use Cases

The Big Idea

What if you could fix a bug once and see it fixed everywhere instantly?

The Scenario

Imagine you have many JavaScript files, each with useful functions or data. Without importing, you must copy and paste the same code everywhere you need it.

The Problem

Copying code manually is slow and risky. If you fix a bug or update a value, you must change it in every file. This causes mistakes and wastes time.

The Solution

Importing lets you write code once and reuse it by bringing values or functions into other files easily. This keeps your code clean, consistent, and easy to update.

Before vs After

✗ Before

export const pi = 3.14;
// copy this in every file needing pi

✓ After

import { pi } from './constants.js';
// use pi directly without copying

What It Enables

Importing values enables building modular, maintainable code where updates happen in one place and reflect everywhere.

Real Life Example

Think of a recipe book: instead of rewriting the same recipe in every chapter, you just refer to it once. If the recipe changes, all chapters get the update automatically.

Key Takeaways

Manual copying causes errors and wastes time.

Importing shares values across files easily.

It keeps code organized and simple to maintain.

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