Dynamic imports with types in Typescript - Mini Project: Build & Apply

Dynamic imports with types

📖 Scenario: You are building a TypeScript app that loads different greeting messages dynamically based on user choice. Each greeting is in a separate module.

🎯 Goal: Create a TypeScript program that dynamically imports greeting modules with proper type annotations and displays the greeting message.

📋 What You'll Learn

Create a type for the greeting module's default export

Use dynamic import() with type annotations

Load a greeting module dynamically based on a variable

Print the greeting message from the imported module

💡 Why This Matters

🌍 Real World

Dynamic imports let apps load code only when needed, saving resources and speeding up startup.

💼 Career

Many modern web apps use dynamic imports with TypeScript to improve performance and maintain type safety.

1

Create greeting modules and type

Create a type called GreetingModule with a default string property. Then create two modules: hello.ts exporting default as "Hello, world!" and hi.ts exporting default as "Hi there!".

Typescript

# Define the GreetingModule type and create hello.ts and hi.ts modules
# Your code here

Hint

Use export type GreetingModule = { default: string }; and create two files with export default strings.

2

Add a variable for the module name

Create a variable called moduleName and set it to the string "hello".

Typescript

export type GreetingModule = { default: string };

// hello.ts
export default "Hello, world!";

// hi.ts
export default "Hi there!";

// Create a variable called moduleName and set it to "hello"
# Your code here

Hint

Use const moduleName = "hello"; to store the module name.

3

Dynamically import the module with type

Use import() with a type annotation to dynamically import the module named by moduleName. Store the result in a variable called greetingModule with type Promise<typeof import("./hello")>.

Typescript

export type GreetingModule = { default: string };

// hello.ts
export default "Hello, world!";

// hi.ts
export default "Hi there!";

const moduleName = "hello";

// Dynamically import the module with type annotation
# Your code here

Hint

Use const greetingModule: Promise<typeof import("./hello")> = import(`./${moduleName}`); to dynamically import with types.

4

Print the greeting message

Use await to get the module from greetingModule and then print the default export using console.log. Wrap the code in an async function called showGreeting and call it.

Typescript

export type GreetingModule = { default: string };

// hello.ts
export default "Hello, world!";

// hi.ts
export default "Hi there!";

const moduleName = "hello";

const greetingModule: Promise = import(`./${moduleName}`);

// Create async function showGreeting to await greetingModule and print default export
# Your code here

Hint

Use an async function to await the import and then console.log(mod.default).

Practice

1. What is the main benefit of using dynamic imports with types in TypeScript?

easy

A. They make the code run faster by compiling to machine code.

B. They load modules only when needed, improving app speed and type safety.

C. They automatically convert JavaScript to TypeScript.

D. They prevent any runtime errors without writing tests.

Solution

1. Step 1: Understand dynamic imports

   Dynamic imports load code only when it is needed, not all at once.

2. Step 2: Understand types with dynamic imports

   Using typeof import() adds type safety, helping catch errors early.

3. Final Answer:

   They load modules only when needed, improving app speed and type safety. -> Option B

4. Quick Check:

   Dynamic imports + types = faster and safer code [OK]

Hint: Dynamic imports delay loading; types keep code safe [OK]

Common Mistakes:

• Thinking dynamic imports compile code faster
• Confusing dynamic imports with automatic type conversion
• Believing dynamic imports prevent all runtime errors

2. Which of the following is the correct syntax to dynamically import a module named utils with types in TypeScript?

easy

A. const utils: typeof import('utils') = await import('utils');

B. const utils = await import('utils');

C. import utils from 'utils';

D. const utils = import('utils');

Solution

1. Step 1: Identify dynamic import syntax

   Dynamic imports use await import('module') inside async functions.

2. Step 2: Add type annotation

   Use const x: typeof import('module') to add types for the imported module.

3. Final Answer:

   const utils: typeof import('utils') = await import('utils'); -> Option A

4. Quick Check:

   Dynamic import with type annotation = const utils: typeof import('utils') = await import('utils'); [OK]

Hint: Use 'const x: typeof import() = await import()' [OK]

Common Mistakes:

• Omitting 'await' in dynamic import
• Using static import syntax for dynamic import
• Not adding type annotation for imported module

3. Consider this TypeScript code inside an async function:

const mod: typeof import('./math') = await import('./math');
const result = mod.add(2, 3);
console.log(result);

If ./math exports export function add(a: number, b: number) { return a + b; }, what will be the output?

medium

A. Type error at compile time

B. undefined

C. Runtime error: mod.add is not a function

D. 5

Solution

1. Step 1: Understand dynamic import with types

   The module is imported dynamically with correct typing, so mod.add is recognized as a function.

2. Step 2: Calculate the function call

   Calling mod.add(2, 3) returns 5, which is logged.

3. Final Answer:

   5 -> Option D

4. Quick Check:

   Dynamic import calls function correctly = 5 [OK]

Hint: Dynamic import with correct type calls function normally [OK]

Common Mistakes:

• Expecting undefined because of dynamic import
• Confusing runtime error with type error
• Forgetting to await the import

4. What is wrong with this TypeScript code snippet?

const mod: typeof import('./utils') = import('./utils');
console.log(mod.helper());

medium

A. Type annotation is incorrect; should not use typeof import().

B. Cannot call console.log inside async code.

C. Missing 'await' before import, so mod is a Promise, not the module.

D. Module './utils' does not exist.

Solution

1. Step 1: Check import usage

   Dynamic import returns a Promise, so it must be awaited to get the module.

2. Step 2: Identify error cause

   Without await, mod is a Promise, so calling mod.helper() causes an error.

3. Final Answer:

   Missing 'await' before import, so mod is a Promise, not the module. -> Option C

4. Quick Check:

   Dynamic import needs await to get module [OK]

Hint: Always await dynamic imports to get the module object [OK]

Common Mistakes:

• Forgetting to await dynamic import
• Misusing type annotation syntax
• Assuming import returns module directly

5. You want to dynamically import a module './config' that exports a default object with a property apiUrl. How do you correctly type and access apiUrl using dynamic imports in TypeScript?

hard

A. const config: typeof import('./config') = await import('./config'); console.log(config.default.apiUrl);

B. const config = await import('./config'); console.log(config.apiUrl);

C. const config: typeof import('./config') = await import('./config'); console.log(config.apiUrl);

D. const config = await import('./config'); console.log(config.default.apiUrl);

Solution

1. Step 1: Understand default exports in dynamic imports

   When a module exports default, it is accessed via the default property on the imported module object.

2. Step 2: Use type annotation and access property

   Typing with typeof import() is correct, and to get apiUrl, use config.default.apiUrl.

3. Final Answer:

   const config: typeof import('./config') = await import('./config'); console.log(config.default.apiUrl); -> Option A

4. Quick Check:

   Default export accessed via .default with type = const config: typeof import('./config') = await import('./config'); console.log(config.default.apiUrl); [OK]

Hint: Default exports accessed via .default after dynamic import [OK]

Common Mistakes:

• Accessing default export directly without .default
• Not using await with import
• Ignoring type annotation for imported module