Deno standard library overview - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the HTTP server module from Deno's standard library.

Deno

import { serve } from "https://deno.land/std/http/[1].ts";

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

Aserve

Bserver

Chttp

Dhttp_server

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'serve' as the module name instead of 'server'.

Using 'http' which is a folder, not a module.

The correct module to import the HTTP server is server from the standard library URL.

2fill in blank

medium

Complete the code to import the path module from Deno's standard library.

Deno

import * as path from "https://deno.land/std/[1]/path/mod.ts";

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

Apath

Bfs

Chttp

Dio

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'fs' which is for file system, not path utilities.

Using 'io' which is for input/output streams.

The path module is located under the path folder in the standard library.

3fill in blank

hard

Fix the error in the import statement to correctly import the colors module.

Deno

import { red } from "https://deno.land/std/fmt/[1].ts";

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

Acolor

Bcolorful

Ccolorize

Dcolors

Attempts:

3 left

💡 Hint

Common Mistakes

Using singular 'color' instead of 'colors'.

Using unrelated folder names like 'colorful'.

The correct folder name for color utilities is colors inside the fmt directory.

4fill in blank

hard

Fill both blanks to import the assertEquals function from the testing module.

Deno

import { [1] } from "https://deno.land/std/testing/[2].ts";

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

AassertEquals

Bassert

Cmod

Dasserts

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'assert' instead of 'assertEquals'.

Using 'mod' as module name instead of 'asserts'.

The function assertEquals is imported from the asserts module inside the testing folder.

5fill in blank

hard

Fill all three blanks to create a simple HTTP server that responds with 'Hello World'.

Deno

import { serve } from "https://deno.land/std/http/[1].ts";

const server = serve({ port: [2] });

for await (const [3] of server) {
  [3].respond({ body: "Hello World" });
}

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

Aserver

B8080

Creq

Dlisten

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong module name like 'listen'.

Using invalid port numbers.

Using variable names other than 'req' for requests.

The HTTP server module is server. The port is commonly set to 8080. The request variable is often named req to handle incoming requests.

Practice

1. What is the main purpose of the Deno standard library?

easy

A. To provide ready-to-use modules for common programming tasks

B. To replace the Deno runtime environment

C. To serve as a database management system

D. To compile TypeScript code into JavaScript

Solution

1. Step 1: Understand the role of a standard library

   A standard library offers pre-built tools and modules to simplify common programming tasks.

2. Step 2: Identify the Deno standard library's purpose

   The Deno standard library provides modules for file handling, HTTP, dates, testing, and more, helping developers avoid writing everything from scratch.

3. Final Answer:

   To provide ready-to-use modules for common programming tasks -> Option A

4. Quick Check:

   Deno standard library = ready-to-use modules [OK]

Hint: Standard libraries offer common tools, not runtime or compilers [OK]

Common Mistakes:

• Confusing the standard library with the runtime environment
• Thinking it compiles code
• Assuming it manages databases

2. Which is the correct way to import a module from the Deno standard library with versioning?

easy

A. import { serve } from "https://deno.land/std@0.200.0/http/server.ts";

B. import serve from "deno.land/std/http/server.ts";

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

D. import * as serve from "https://deno.land/std@latest/http/server.ts";

Solution

1. Step 1: Check the import URL format for Deno standard library

   The URL must include the version number after @ to ensure stability, e.g., @0.200.0.

2. Step 2: Verify the import syntax

   Correct syntax uses named imports with curly braces and a full URL including version.

3. Final Answer:

   import { serve } from "https://deno.land/std@0.200.0/http/server.ts"; -> Option A

4. Quick Check:

   Versioned URL + named import = import { serve } from "https://deno.land/std@0.200.0/http/server.ts"; [OK]

Hint: Always include @version in URL for stable imports [OK]

Common Mistakes:

• Omitting the version number in the URL
• Using incorrect import syntax without braces
• Using 'latest' instead of a fixed version

3. What will the following code output?

import { format } from "https://deno.land/std@0.200.0/datetime/mod.ts";
const date = new Date("2024-06-15T12:00:00Z");
console.log(format(date, "yyyy-MM-dd"));

medium

A. 06-15-2024

B. 2024-06-15

C. 15-06-2024

D. 2024/06/15

Solution

1. Step 1: Understand the format function usage

   The format function formats a Date object according to the pattern string provided.

2. Step 2: Analyze the pattern "yyyy-MM-dd"

   "yyyy" means 4-digit year, "MM" means 2-digit month, "dd" means 2-digit day, separated by dashes.

3. Final Answer:

   2024-06-15 -> Option B

4. Quick Check:

   Date formatted as yyyy-MM-dd = 2024-06-15 [OK]

Hint: Match format pattern exactly to output date string [OK]

Common Mistakes:

• Mixing day and month order
• Using slashes instead of dashes
• Ignoring the format string

4. Identify the error in this Deno standard library import:

import { assertEquals } from "https://deno.land/std/testing/asserts.ts";
assertEquals(1 + 1, 2);

medium

A. Incorrect import syntax, should use default import

B. assertEquals is not a valid function

C. Missing version number in the import URL

D. assertEquals requires async function

Solution

1. Step 1: Check the import URL for versioning

   The URL lacks a version number after @, which is required for stable imports in Deno.

2. Step 2: Confirm the function and syntax

   assertEquals is a valid named export and the import syntax is correct; no async needed here.

3. Final Answer:

   Missing version number in the import URL -> Option C

4. Quick Check:

   Version number missing in URL = Missing version number in the import URL [OK]

Hint: Always check for @version in import URLs [OK]

Common Mistakes:

• Assuming assertEquals is invalid
• Thinking default import is required
• Believing assertEquals needs async

5. You want to create a simple HTTP server using Deno's standard library that responds with "Hello World". Which code snippet correctly uses the standard library's HTTP module with versioning?

hard

A. import { serve } from "https://deno.land/std@0.200.0/http/server.ts";
serve(() => Response.json({message: "Hello World"}));

B. import serve from "https://deno.land/std/http/server.ts";
serve(() => new Response("Hello World"));

C. import { serve } from "https://deno.land/std@0.200.0/http/server.ts";
serve(request => Response.text("Hello World"));

D. import { serve } from "https://deno.land/std@0.200.0/http/server.ts";
serve(() => new Response("Hello World"));

Solution

1. Step 1: Verify import URL and syntax

   import { serve } from "https://deno.land/std@0.200.0/http/server.ts"; serve(() => new Response("Hello World")); correctly imports serve with a versioned URL and uses named import syntax.

2. Step 2: Check the serve function usage

   serve expects a function returning a Response object; new Response("Hello World") is correct.

3. Step 3: Evaluate other options

   import serve from "https://deno.land/std/http/server.ts"; serve(() => new Response("Hello World")); lacks versioning; import { serve } from "https://deno.land/std@0.200.0/http/server.ts"; serve(request => Response.text("Hello World")); uses incorrect Response method; import { serve } from "https://deno.land/std@0.200.0/http/server.ts"; serve(() => Response.json({message: "Hello World"})); returns JSON, not plain text.

4. Final Answer:

   import { serve } from "https://deno.land/std@0.200.0/http/server.ts"; serve(() => new Response("Hello World")); -> Option D

5. Quick Check:

   Versioned import + correct Response = import { serve } from "https://deno.land/std@0.200.0/http/server.ts"; serve(() => new Response("Hello World")); [OK]

Hint: Use versioned import and new Response("text") for HTTP server [OK]

Common Mistakes:

• Omitting version number in import URL
• Using incorrect Response methods
• Wrong import syntax