Deno standard library overview - Performance & Optimization

Performance: Deno standard library overview

MEDIUM IMPACT

This affects the initial load time and runtime performance by controlling which utilities and modules are included and how they are loaded.

Importing utilities from the Deno standard library

Deno

import { readFileSync } from "https://deno.land/std@0.203.0/fs/mod.ts";

const data = readFileSync("file.txt");

Imports only the needed function, reducing network load and parsing time.

📈 Performance GainSaves 400kb+ in bundle size, faster startup and execution

Importing utilities from the Deno standard library

Deno

import * as std from "https://deno.land/std@0.203.0/mod.ts";

const data = std.fs.readFileSync("file.txt");

Imports the entire standard library module, increasing load time and memory usage unnecessarily.

📉 Performance CostAdds 500kb+ to initial load, blocks execution until full module is fetched

Performance Comparison

Pattern	Module Size	Fetch Time	Compile Time	Verdict
Import entire std library	Large (500kb+)	High (blocks startup)	High (parsing large code)	[X] Bad
Import specific std module	Small (few kb)	Low (fast fetch)	Low (quick compile)	[OK] Good

Rendering Pipeline

Deno fetches and compiles imported modules before running code. Large or unnecessary imports increase fetch and compile time, delaying execution.

→Module Fetch

→Compile

→Execute

⚠️ BottleneckModule Fetch and Compile due to large or unoptimized imports

Core Web Vital Affected

LCP

This affects the initial load time and runtime performance by controlling which utilities and modules are included and how they are loaded.

Optimization Tips

1Import only the specific modules or functions you need from the Deno standard library.

2Avoid importing the entire standard library to reduce load and compile time.

3Use the Network panel in DevTools to monitor module fetch sizes and optimize imports.

Performance Quiz - 3 Questions

What is the main performance benefit of importing specific modules from the Deno standard library instead of the entire library?

A Allows using deprecated APIs

B Reduces network load and speeds up startup

C Improves runtime memory usage by caching all modules

D Automatically updates modules to latest versions

DevTools: Network

How to check: Open DevTools Network panel, reload the Deno script, and observe the size and number of fetched modules.

What to look for: Look for large module files or many unnecessary imports increasing load time.

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