Dynamic imports with types in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a dynamic import in TypeScript?

A dynamic import is a way to load modules asynchronously at runtime using the <code>import()</code> function, allowing code to be split and loaded only when needed.

intermediate

How do you specify types when using dynamic imports in TypeScript?

You can specify types by using import() with a type assertion or by importing the module type separately and then asserting the imported module's shape.

intermediate

Why use dynamic imports with types instead of static imports?

Dynamic imports help reduce initial load time by loading code only when needed, and using types ensures type safety and better developer experience with autocompletion and error checking.

beginner

Show a simple example of a dynamic import with type in TypeScript.

Example:<br><pre>type ModuleType = { greet: () => void };
const module = await import('./module') as ModuleType;
module.greet();</pre>

intermediate

What happens if the dynamically imported module does not match the expected type?

TypeScript will show a type error during development if the module does not match the expected type, helping catch mistakes early before running the code.

What syntax is used for dynamic imports in TypeScript?

A include('./module')

B require('./module')

C import './module'

D import('./module')

Dynamic imports use the import() function syntax to load modules asynchronously.

How can you ensure type safety when using dynamic imports?

A Use type assertions or import types separately

B Use <code>any</code> type

C Ignore types for dynamic imports

D Use <code>require()</code> instead

Type assertions or importing types separately help ensure type safety with dynamic imports.

What is a benefit of dynamic imports?

A Make code run synchronously

B Load code only when needed

C Disable type checking

D Increase initial bundle size

Dynamic imports allow loading code only when needed, improving performance.

Which keyword is NOT used with dynamic imports?

A require

B import

C await

D as

require is CommonJS syntax, not used for dynamic imports in TypeScript.

What does this code do? const mod = await import('./mod') as { foo: () => void };

A Imports './mod' synchronously

B Statically imports './mod' without types

C Dynamically imports './mod' and asserts it has a foo function

D Throws an error always

This code dynamically imports the module and asserts it has a function named foo.

Explain how to use dynamic imports with types in TypeScript and why it is useful.

Think about loading code only when needed and keeping type checks.

Describe a simple example of a dynamic import with a type assertion in TypeScript.

Show how to load a module and tell TypeScript what shape it has.

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