Importing from URLs in Deno - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Deno module import?

Consider this Deno code that imports a function from a URL and uses it.

What will be printed when this code runs?

Deno

import { greet } from "https://example.com/utils/greet.ts";

console.log(greet("Alice"));

A "Hello, Alice!"

B "greet is not a function"

C SyntaxError: Invalid import statement

D ReferenceError: greet is not defined

💡 Hint

Think about how Deno supports importing modules directly from URLs.

Deno allows importing modules directly from URLs. If the URL exports a function named greet, it can be imported and used as shown. The output will be the string returned by greet with the argument "Alice".

📝 Syntax

intermediate

Which import statement is valid in Deno for importing from a URL?

Select the correct syntax to import the default export from a URL module in Deno.

A import * as greet from "https://example.com/greet.ts";

B import greet from "https://example.com/greet.ts";

C import { greet } from "https://example.com/greet.ts";

D import greet() from "https://example.com/greet.ts";

💡 Hint

Default exports are imported without braces.

To import a default export, use `import name from 'url';`. Named exports require braces. The syntax with parentheses is invalid.

🔧 Debug

advanced

Why does this Deno import from URL fail at runtime?

This code tries to import a function from a URL but throws an error at runtime.

What is the most likely cause?

Deno

import { calculate } from "https://example.com/math.ts";

console.log(calculate(5));

A The remote module does not export a function named calculate.

B The URL does not end with .ts or .js extension, causing Deno to reject it.

C Deno does not support importing from HTTPS URLs.

D The import statement must use require() instead of import.

💡 Hint

Check what the remote module exports.

If the remote module does not export the named function calculate, the import will fail at runtime with an error that calculate is undefined.

❓ state_output

advanced

What is the value of variable 'result' after this import and call?

Given this Deno code importing from a URL, what is the value of 'result' after execution?

Deno

import { double } from "https://example.com/utils.ts";

const result = double(4);

A ReferenceError: double is not defined

B 4

C 8

D NaN

💡 Hint

Assume the remote module exports a function that doubles the input number.

The imported function double multiplies the input by 2. Calling double(4) returns 8, so result is 8.

🧠 Conceptual

expert

Which statement about importing modules from URLs in Deno is TRUE?

Select the true statement about how Deno handles imports from URLs.

A Deno automatically updates remote modules every time the program runs.

B Deno requires manual downloading of remote modules before importing them.

C Deno only supports importing from local file paths, not URLs.

D Deno caches remote modules locally after first download to avoid repeated network requests.

💡 Hint

Think about how Deno optimizes repeated imports from the same URL.

Deno caches remote modules locally after the first download. This speeds up subsequent runs and avoids unnecessary network calls. It does not require manual downloads or update modules automatically every run.

Practice

1. What is the main benefit of importing modules from URLs in Deno?

easy

A. You can use code directly from the web without installing it locally.

B. It makes your code run faster than local imports.

C. It automatically updates your code to the latest version.

D. It disables caching to always fetch fresh code.

Solution

1. Step 1: Understand URL imports in Deno

   Deno allows importing modules directly from web URLs, so you don't need to install packages locally.

2. Step 2: Identify the main benefit

   This feature simplifies using external code by fetching it on demand without manual installs.

3. Final Answer:

   You can use code directly from the web without installing it locally. -> Option A

4. Quick Check:

   Importing from URLs = No local install needed [OK]

Hint: Remember: URL imports mean no local installs needed [OK]

Common Mistakes:

• Thinking URL imports always update to latest code
• Believing URL imports disable caching
• Assuming URL imports make code run faster

2. Which of the following is the correct syntax to import a module from a URL in Deno?

easy

A. import { serve } from "https://deno.land/std/http/server.ts";

B. require("https://deno.land/std/http/server.ts");

C. import serve from "./server.ts";

D. load { serve } from "https://deno.land/std/http/server.ts";

Solution

1. Step 1: Recall Deno import syntax

   Deno uses ES module syntax with import { ... } from "url"; to import from URLs.

2. Step 2: Check each option

   import { serve } from "https://deno.land/std/http/server.ts"; uses correct ES module import syntax with a URL. require("https://deno.land/std/http/server.ts"); uses Node.js style require, which Deno does not use. import serve from "./server.ts"; imports locally, not from URL. load { serve } from "https://deno.land/std/http/server.ts"; uses invalid keyword load.

3. Final Answer:

   import { serve } from "https://deno.land/std/http/server.ts"; -> Option A

4. Quick Check:

   Correct import syntax = import { serve } from "https://deno.land/std/http/server.ts"; [OK]

Hint: Deno uses ES import syntax, not require or load [OK]

Common Mistakes:

• Using require() instead of import
• Trying to import local files with URL syntax
• Using invalid keywords like load

3. What will happen when you run this Deno code snippet?

import { serve } from "https://deno.land/std/http/server.ts";

console.log(typeof serve);

medium

A. "object"

B. "undefined"

C. Runtime error: Module not found

D. "function"

Solution

1. Step 1: Understand what is imported

   The serve function is exported from the URL module as a function.

2. Step 2: Check the typeof operator on serve

   Since serve is a function, typeof serve returns the string "function".

3. Final Answer:

   "function" -> Option D

4. Quick Check:

   typeof serve = "function" [OK]

Hint: Imported functions have typeof 'function' in JS/TS [OK]

Common Mistakes:

• Expecting 'undefined' if module loads correctly
• Thinking import causes runtime error
• Confusing function with object type

4. Identify the error in this Deno import statement:

import { serve } from "https://deno.land/std/http/server";

medium

A. URL must start with http:// not https://.

B. Using curly braces {} around serve is incorrect.

C. Missing file extension ".ts" in the URL.

D. Cannot import from URLs in Deno.

Solution

1. Step 1: Check URL correctness

   Deno requires full file paths including extensions for URL imports, so missing ".ts" causes error.

2. Step 2: Validate other parts

   Curly braces are correct for named imports. HTTPS is supported. Deno supports URL imports.

3. Final Answer:

   Missing file extension ".ts" in the URL. -> Option C

4. Quick Check:

   File extension required in URL imports [OK]

Hint: Always include file extensions in Deno URL imports [OK]

Common Mistakes:

• Omitting file extensions in import URLs
• Thinking HTTPS is unsupported
• Misunderstanding import syntax with braces

5. You want to ensure your Deno project always uses the same version of a library imported from a URL. Which practice helps achieve this?

hard

A. Disable Deno's cache to force fresh downloads every run.

B. Use a versioned URL like "https://deno.land/std@0.203.0/http/server.ts".

C. Manually download and import local copies only.

D. Import from the base URL without version to get latest updates.

Solution

1. Step 1: Understand versioning in URL imports

   Using versioned URLs locks the imported code to a specific release, ensuring stability.

2. Step 2: Evaluate options

   Use a versioned URL like "https://deno.land/std@0.203.0/http/server.ts". uses a versioned URL, which is best practice. Import from the base URL without version to get latest updates. fetches latest, risking breaking changes. Manually download and import local copies only. is manual and not URL import. Disable Deno's cache to force fresh downloads every run. disables caching, causing inefficiency.

3. Final Answer:

   Use a versioned URL like "https://deno.land/std@0.203.0/http/server.ts". -> Option B

4. Quick Check:

   Versioned URLs = stable imports [OK]

Hint: Lock versions in URL to keep imports stable [OK]

Common Mistakes:

• Using unversioned URLs expecting stability
• Disabling cache wastes time and bandwidth
• Confusing manual local imports with URL imports