Compatibility gaps and workarounds in Deno - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import a Node.js module in Deno using compatibility mode.

Deno

import express from '[1]';

Drag options to blanks, or click blank then click option'

Anode:express

Bhttps://deno.land/std/express

Cnpm:express

D./express.js

Attempts:

3 left

💡 Hint

Common Mistakes

Using a URL instead of npm prefix for Node.js modules.

Trying to import Node.js modules without compatibility mode.

In Deno, to import Node.js modules, you prefix the module name with npm: to use compatibility mode.

2fill in blank

medium

Complete the code to enable Node.js compatibility in Deno configuration.

Deno

"compat": { "[1]": true }

Drag options to blanks, or click blank then click option'

AnodeModules

Bnode

CnodeCompat

DnodeCompatibility

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect keys like 'nodeModules' or 'nodeCompat'.

Forgetting to enable compatibility in config.

In Deno's configuration, setting compat.node to true enables Node.js compatibility.

3fill in blank

hard

Fix the error in the code to import a Node.js built-in module in Deno.

Deno

import path from '[1]';

Drag options to blanks, or click blank then click option'

Apath

Bnpm:path

Chttps://deno.land/std/path/mod.ts

Dnode:path

Attempts:

3 left

💡 Hint

Common Mistakes

Using npm prefix for built-in modules.

Using URL imports for Node.js built-ins.

Deno supports Node.js built-in modules by prefixing with node:. So node:path imports the Node.js path module.

4fill in blank

hard

Fill both blanks to create a Deno script that uses a Node.js module with compatibility enabled.

Deno

import [1] from '[2]';

console.log([1]());

Drag options to blanks, or click blank then click option'

Aexpress

Bnpm:express

Cpath

Dnode:path

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping variable name and import path.

Using 'node:path' for express module.

To use a Node.js module like express in Deno, import it with the npm prefix and use the module name as the import variable.

5fill in blank

hard

Fill all three blanks to create a Deno script that imports a Node.js built-in module and uses a function.

Deno

import [1] from '[2]';

const fullPath = [3].join('home', 'user', 'docs');
console.log(fullPath);

Drag options to blanks, or click blank then click option'

Apath

Bnode:path

Cjoin

Dnpm:path

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'npm:path' instead of 'node:path' for built-in modules.

Using wrong variable names or function names.

Import the Node.js built-in 'path' module with 'node:path'. Use the variable 'path' and call its 'join' method.

Practice

1. Which statement best describes how Deno handles module imports compared to Node.js?

easy

A. Deno uses URL-based ES module imports instead of Node.js package imports.

B. Deno uses CommonJS require() for all modules like Node.js.

C. Deno imports modules only from local files, not URLs.

D. Deno automatically converts Node.js packages to ES modules.

Solution

1. Step 1: Understand Deno's import style

   Deno uses ES modules imported via URLs or local paths, unlike Node.js which uses package names with require().

2. Step 2: Compare with Node.js imports

   Node.js uses CommonJS require() or ES modules with package names resolved from node_modules, which Deno does not support by default.

3. Final Answer:

   Deno uses URL-based ES module imports instead of Node.js package imports. -> Option A

4. Quick Check:

   Import style difference = A [OK]

Hint: Remember: Deno imports from URLs, Node.js from packages [OK]

Common Mistakes:

• Thinking Deno supports require() like Node.js
• Assuming Deno imports only local files
• Believing Deno auto-converts Node packages

2. Which of the following is the correct way to import the "path" module in Deno?

easy

A. import path from "path";

B. const path = require("path");

C. import * as path from "https://deno.land/std/path/mod.ts";

D. import { path } from "node:path";

Solution

1. Step 1: Identify Deno's standard library import method

   Deno imports standard modules via URLs from its official repository, e.g., https://deno.land/std/path/mod.ts.

2. Step 2: Check each option

   import path from "path"; uses Node.js style import without URL, invalid in Deno. const path = require("path"); uses require(), not supported in Deno. import { path } from "node:path"; uses Node.js built-in module specifier, not valid in Deno.

3. Final Answer:

   import * as path from "https://deno.land/std/path/mod.ts"; -> Option C

4. Quick Check:

   Standard library import = D [OK]

Hint: Deno imports std modules via full URLs [OK]

Common Mistakes:

• Using require() instead of import
• Omitting the full URL for std modules
• Trying to import Node.js built-ins directly

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

import { readFileStr } from "https://deno.land/std/fs/mod.ts";

const data = await readFileStr("./example.txt");
console.log(data);

Assuming "example.txt" contains the text "Hello Deno!".

medium

A. undefined

B. "Hello Deno!"

C. SyntaxError due to await outside async

D. Error: Module not found

Solution

1. Step 1: Understand the code behavior

   The code imports readFileStr from Deno's standard fs module and reads the file content asynchronously.

2. Step 2: Check for syntax and runtime correctness

   The code uses top-level await, which Deno supports. The file exists with content "Hello Deno!" so readFileStr returns that string.

3. Final Answer:

   "Hello Deno!" -> Option B

4. Quick Check:

   File read content = A [OK]

Hint: Deno supports top-level await for async calls [OK]

Common Mistakes:

• Assuming await needs async function wrapper
• Confusing readFileStr with returning undefined
• Thinking module URL is invalid

4. You try to use the Node.js "crypto" module in Deno with import crypto from "crypto"; but get an error. What is the best way to fix this?

medium

A. Install Node.js crypto package via npm and import it.

B. Add a --allow-node-compat flag to Deno run command.

C. Change import to import * as crypto from "crypto";.

D. Use Deno's built-in Web Crypto API instead of Node.js crypto.

Solution

1. Step 1: Identify compatibility issue

   Deno does not support Node.js built-in modules like "crypto" directly, so importing "crypto" fails.

2. Step 2: Use Deno's alternative

   Deno provides the Web Crypto API natively, which covers most cryptographic needs securely and without extra packages.

3. Final Answer:

   Use Deno's built-in Web Crypto API instead of Node.js crypto. -> Option D

4. Quick Check:

   Use Web Crypto API = B [OK]

Hint: Use Deno's Web Crypto, not Node.js crypto module [OK]

Common Mistakes:

• Trying to import Node.js crypto directly
• Assuming npm packages work without compatibility layer
• Using wrong import syntax for Node.js modules

5. You want to use a popular Node.js library that depends on "fs" and "path" modules in your Deno project. Which approach best handles this compatibility gap?

hard

A. Use a compatibility layer like "deno_std/node" to shim Node.js modules.

B. Rewrite the library code to remove all Node.js dependencies.

C. Run the Node.js library in a separate Node.js process and communicate via IPC.

D. Import the Node.js modules directly using Deno's native support.

Solution

1. Step 1: Understand the problem

   Node.js libraries often rely on built-in modules like "fs" and "path" which Deno does not support natively.

2. Step 2: Identify Deno's workaround

   Deno provides a compatibility layer "deno_std/node" that shims many Node.js modules to allow such libraries to run with minimal changes.

3. Final Answer:

   Use a compatibility layer like "deno_std/node" to shim Node.js modules. -> Option A

4. Quick Check:

   Use compatibility shim = C [OK]

Hint: Use deno_std/node for Node.js module compatibility [OK]

Common Mistakes:

• Trying to import Node.js modules directly
• Assuming full rewrite is always needed
• Ignoring IPC as a complex alternative