Deno standard library overview - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Deno standard library?

The Deno standard library is a collection of tested, reviewed, and maintained modules that come with Deno. It provides useful tools and utilities for common tasks like working with files, dates, HTTP servers, and more, so you don't have to write everything from scratch.

beginner

Name three common modules found in the Deno standard library.

Three common modules are:
1. fs for file system operations
2. http for creating HTTP servers
3. datetime for working with dates and times

beginner

How do you import a module from the Deno standard library?

You import a module by using a URL that points to the Deno standard library repository with a version number. For example:<br><code>import { serve } from "https://deno.land/std@0.203.0/http/server.ts";</code><br>This loads the HTTP server module.

intermediate

Why is it good to use the Deno standard library instead of third-party modules?

The Deno standard library is maintained by the Deno team, so it is reliable, secure, and well tested. It also matches Deno's design and updates regularly. Using it helps keep your code safe and consistent.

intermediate

What is the role of the testing module in the Deno standard library?

The testing module helps you write and run tests for your code. It provides functions to check if your code works as expected, making it easier to find and fix bugs early.

Which URL format is used to import modules from the Deno standard library?

A https://github.com/deno/module

B https://deno.land/std@version/module.ts

C https://cdn.jsdelivr.net/npm/module

D https://npmjs.com/package/module

Deno standard library modules are imported using URLs like https://deno.land/std@version/module.ts.

Which module would you use to create an HTTP server in Deno?

A fs

B datetime

C http

D testing

The 'http' module in the Deno standard library provides tools to create HTTP servers.

What is a key advantage of using the Deno standard library?

A It is maintained by the Deno team and well tested.

B It requires no internet connection.

C It only works with Node.js.

D It automatically updates your code.

The Deno standard library is maintained by the Deno team, ensuring reliability and security.

Which module helps with file system operations in Deno's standard library?

A fs

B http

C testing

D path

The 'fs' module provides functions to work with files and directories.

How do you specify the version of the Deno standard library when importing a module?

A By importing from npm

B By setting an environment variable

C By using a config file

D By adding @version after std in the URL

You specify the version by adding @version after 'std' in the import URL, like std@0.203.0.

Explain what the Deno standard library is and why it is useful.

Think about how it helps you avoid writing common code yourself.

Describe how to import and use a module from the Deno standard library in your code.

Remember the URL format and versioning.

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