Node.js built-in module support in Deno - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of Node.js built-in modules?

Node.js built-in modules provide ready-to-use features like file handling, networking, and streams without needing extra installation.

intermediate

How does Deno support Node.js built-in modules?

Deno supports many Node.js built-in modules by providing compatibility layers or polyfills, allowing code using Node.js modules to run in Deno.

intermediate

Show how to import the 'fs' module in Node.js and its equivalent in Deno.

In Node.js: <code>import fs from 'fs';</code><br>In Deno: <code>import * as fs from 'node:fs';</code> or use Deno's native <code>Deno.readFile</code> APIs.

advanced

Why might some Node.js built-in modules not work perfectly in Deno?

Because Deno has different security, APIs, and runtime design, some Node.js modules may lack full support or behave differently.

beginner

What command enables Node.js compatibility in Deno?

Running Deno with the --unstable flag enables Node.js compatibility mode.

Which flag enables Node.js compatibility in Deno?

A --polyfill

B --unstable

C --legacy

D --node

The --unstable flag enables Node.js compatibility mode in Deno.

How do you import the 'path' module from Node.js in Deno?

A import path from 'path';

B import path from 'deno:path';

C import * as path from 'node:path';

D import * as path from 'fs:path';

Deno uses the node: prefix to import Node.js built-in modules, so import * as path from 'node:path'; is correct.

Why might some Node.js modules not work fully in Deno?

A Deno has different security and runtime design.

B Deno does not support JavaScript.

C Node.js modules are written in Python.

D Deno only supports browser APIs.

Deno's different security model and runtime design can cause some Node.js modules to not work fully.

Which of these is NOT a Node.js built-in module?

A express

B http

C fs

D path

express is a third-party library, not a built-in module.

What is a benefit of using Node.js built-in modules?

A They are only for frontend development.

B They slow down your app.

C They are written in CSS.

D They require no installation and are ready to use.

Built-in modules come with Node.js and need no extra installation.

Explain how Deno supports Node.js built-in modules and what flags are needed to enable this support.

Think about how Deno runs Node.js code and what command line options help.

Describe the difference between importing a Node.js built-in module in Node.js versus in Deno.

Focus on how the import statement changes.

Practice

1. What is the correct way to import the Node.js built-in path module in Deno?

easy

A. import * as path from "deno_path";

B. import path from "path";

C. import { path } from "deno:path";

D. import path from "node:path";

Solution

1. Step 1: Understand Deno's Node.js module import syntax

   Deno uses the "node:" prefix to import Node.js built-in modules.

2. Step 2: Apply correct import statement for path

   The correct import is import path from "node:path"; to access Node.js path module in Deno.

3. Final Answer:

   import path from "node:path"; -> Option D

4. Quick Check:

   Node.js built-in modules use "node:" prefix in Deno [OK]

Hint: Use "node:" prefix to import Node.js built-ins in Deno [OK]

Common Mistakes:

• Omitting the "node:" prefix
• Using "deno:" prefix instead
• Trying to import from "path" without prefix
• Using incorrect module names

2. Which of the following is the correct syntax to import the Node.js fs module in Deno?

easy

A. import * as fs from "node:fs";

B. import { fs } from "node:fs";

C. import fs from "fs";

D. import fs from "deno:fs";

Solution

1. Step 1: Recall import style for Node.js modules in Deno

   Deno requires the "node:" prefix and supports namespace import for modules like fs.

2. Step 2: Choose correct import syntax for fs

   The correct syntax is import * as fs from "node:fs"; to import all fs exports as a namespace.

3. Final Answer:

   import * as fs from "node:fs"; -> Option A

4. Quick Check:

   Namespace import with "node:" prefix is correct [OK]

Hint: Use namespace import with "node:" prefix for modules like fs [OK]

Common Mistakes:

• Using default import for modules that export multiple members
• Omitting the "node:" prefix
• Trying to destructure import incorrectly
• Using "deno:" prefix

3. What will be the output of the following Deno code snippet?

import { join } from "node:path";
const fullPath = join("/home", "user", "docs");
console.log(fullPath);

medium

A. /home\user\docs

B. /home/user/docs

C. home/user/docs

D. Error: Module not found

Solution

1. Step 1: Understand join from Node.js path module

   The join function combines path segments using the correct separator for the OS.

2. Step 2: Analyze the given path segments

   Segments "/home", "user", "docs" joined on Unix-like OS produce "/home/user/docs".

3. Final Answer:

   /home/user/docs -> Option B

4. Quick Check:

   Node.js path.join joins segments with OS separator [OK]

Hint: Node.js path.join joins paths with OS-specific separator [OK]

Common Mistakes:

• Assuming Windows separator on Unix
• Expecting error due to import
• Confusing join with concat
• Ignoring leading slash in first segment

4. Identify the error in this Deno code importing Node.js buffer module:

import { Buffer } from "buffer";
const buf = Buffer.from("hello");
console.log(buf.toString());

medium

A. Missing "node:" prefix in import path

B. Buffer is not exported from Node.js buffer module

C. Buffer.from is not a function

D. toString() method does not exist on Buffer

Solution

1. Step 1: Check import path for Node.js built-in modules in Deno

   Deno requires the "node:" prefix to import Node.js built-in modules like buffer.

2. Step 2: Identify the missing prefix causing module resolution error

   Importing from "buffer" without "node:" prefix will fail in Deno.

3. Final Answer:

   Missing "node:" prefix in import path -> Option A

4. Quick Check:

   Always use "node:" prefix for Node.js built-ins in Deno [OK]

Hint: Always prefix Node.js modules with "node:" in Deno imports [OK]

Common Mistakes:

• Omitting the "node:" prefix
• Assuming default import works without prefix
• Confusing Deno modules with Node.js modules
• Misunderstanding Buffer API

5. You want to use the Node.js events module in Deno to create an event emitter. Which code snippet correctly imports and uses it?

hard

A. import EventEmitter from "node:events";
const emitter = new EventEmitter();

B. import { EventEmitter } from "node:events";
const emitter = new events.EventEmitter();

C. import * as events from "node:events";
const emitter = new events.EventEmitter();

D. import events from "events";
const emitter = new events.EventEmitter();

Solution

1. Step 1: Understand how Node.js events module exports EventEmitter

   The events module exports EventEmitter as a named export, so namespace import is common.

2. Step 2: Check correct import syntax with "node:" prefix and usage

   Using import * as events from "node:events"; then new events.EventEmitter() is correct in Deno.

3. Final Answer:

   import * as events from "node:events"; const emitter = new events.EventEmitter(); -> Option C

4. Quick Check:

   Namespace import with "node:" prefix for EventEmitter [OK]

Hint: Use namespace import for EventEmitter from "node:events" [OK]

Common Mistakes:

• Using default import for EventEmitter
• Omitting "node:" prefix
• Importing from "events" without prefix
• Trying to destructure EventEmitter incorrectly