Why Deno bundles development tools - See It in Action

Why Deno Bundles Development Tools

📖 Scenario: You are learning about Deno, a modern JavaScript and TypeScript runtime. Unlike some other runtimes, Deno comes with many development tools built-in. This helps developers write, test, and run code easily without installing many extra tools.

🎯 Goal: Understand and demonstrate why Deno bundles development tools by creating a simple Deno script, configuring a lint rule, running a test, and bundling the code into a single file.

📋 What You'll Learn

Create a simple Deno script file named app.ts with a function that returns a greeting string.

Add a Deno lint configuration to enable the no-explicit-any rule.

Write a test function in app_test.ts to check the greeting function.

Bundle the app.ts file into a single JavaScript file named bundle.js using deno emit.

💡 Why This Matters

🌍 Real World

Deno's bundling of development tools makes it easier for developers to start projects quickly without managing many dependencies. This is helpful in real projects where setup time matters.

💼 Career

Knowing how to use Deno's built-in tools is valuable for modern JavaScript/TypeScript development jobs, especially for backend and full-stack roles that use Deno.

1

Create a simple Deno script

Create a file named app.ts and write a function called greet that takes a name string parameter and returns the string `Hello, ${name}!`.

Deno

// Your code here

Hint

Use a TypeScript function with a string parameter and return a template string greeting.

2

Add a Deno lint configuration

Create a file named deno.json and add a lint section with rules that enable no-explicit-any set to true.

Deno

export function greet(name: string): string {
  return `Hello, ${name}!`;
}

// Your code here

Hint

The deno.json file is a JSON file where you add lint rules under the lint.rules key.

3

Write a test for the greet function

Create a file named app_test.ts and write a test using Deno's built-in test function named testGreet. Inside, assert that greet('Deno') returns 'Hello, Deno!'.

Deno

export function greet(name: string): string {
  return `Hello, ${name}!`;
}

{
  "lint": {
    "rules": {
      "no-explicit-any": true
    }
  }
}

// Your code here

Hint

Use Deno.test and import assertEquals from Deno's standard testing library.

4

Bundle the app.ts file

Use Deno's emit command to bundle app.ts into a single JavaScript file named bundle.js. Add a comment line in a file named bundle_command.sh with the exact command deno emit app.ts -o bundle.js.

Deno

export function greet(name: string): string {
  return `Hello, ${name}!`;
}

{
  "lint": {
    "rules": {
      "no-explicit-any": true
    }
  }
}

import { assertEquals } from "https://deno.land/std@0.203.0/testing/asserts.ts";
import { greet } from "./app.ts";

Deno.test("testGreet", () => {
  assertEquals(greet("Deno"), "Hello, Deno!");
});

// Your code here

Hint

Write the emit command as a comment exactly as deno emit app.ts -o bundle.js.

Practice

1. Why does Deno include development tools like formatter, linter, and test runner by default?

easy

A. To require installing many separate packages manually

B. To make the runtime slower and more complex

C. To force developers to use only Deno-specific code

D. To help developers start projects quickly without extra setup

Solution

1. Step 1: Understand Deno's design goal

   Deno aims to simplify development by bundling tools so you don't need extra installs.

2. Step 2: Identify the benefit of bundled tools

   This helps developers start coding quickly and keeps tools consistent across projects.

3. Final Answer:

   To help developers start projects quickly without extra setup -> Option D

4. Quick Check:

   Bundled tools = faster setup [OK]

Hint: Bundled tools mean less setup hassle [OK]

Common Mistakes:

• Thinking Deno slows down by bundling tools
• Believing Deno forces special code
• Assuming manual installs are needed

2. Which command runs tests in Deno without installing extra tools?

easy

A. deno test

B. deno run test.js

C. deno install test

D. deno lint

Solution

1. Step 1: Recall Deno's built-in commands

   Deno includes a test runner accessible by the command deno test.

2. Step 2: Compare options

   deno run test.js runs a script but doesn't run tests specially; deno install test tries to install a tool which is unnecessary; deno lint checks code style, not tests.

3. Final Answer:

   deno test -> Option A

4. Quick Check:

   Run tests = deno test [OK]

Hint: Use 'deno test' to run tests directly [OK]

Common Mistakes:

• Using 'deno run' to run tests
• Trying to install test tools manually
• Confusing lint with test commands

3. What will happen if you run deno fmt on your code in a Deno project?

medium

A. It will show syntax errors without changing code

B. It will format your code automatically to a standard style

C. It will install formatting tools first

D. It will run your code as a script

Solution

1. Step 1: Understand the purpose of deno fmt

   This command formats code files automatically using Deno's built-in formatter.

2. Step 2: Eliminate other options

   It does not run code (that's deno run), nor does it install tools first because tools are bundled, and it does not just show errors without formatting.

3. Final Answer:

   It will format your code automatically to a standard style -> Option B

4. Quick Check:

   deno fmt = auto format code [OK]

Hint: deno fmt cleans code style fast [OK]

Common Mistakes:

• Thinking deno fmt runs code
• Assuming formatter needs install
• Confusing lint errors with formatting

4. You run deno lint but get an error saying command not found. What is the likely cause?

medium

A. Your code has syntax errors

B. You forgot to install the lint tool manually

C. You are using an old Deno version without bundled lint tool

D. You need to run deno fmt first

Solution

1. Step 1: Check Deno version and bundled tools

   Older Deno versions did not include linting by default, so the command may not exist.

2. Step 2: Understand that manual install is not needed in modern Deno

   Since Deno bundles tools now, manual install is unnecessary; syntax errors or formatting do not cause command not found errors.

3. Final Answer:

   You are using an old Deno version without bundled lint tool -> Option C

4. Quick Check:

   Old Deno lacks lint command [OK]

Hint: Check Deno version if lint command missing [OK]

Common Mistakes:

• Assuming manual install is always needed
• Blaming code errors for missing commands
• Thinking formatting fixes lint command

5. You want to ensure your Deno project code is consistent and error-free without installing extra tools. Which approach best uses Deno's bundled tools?

hard

A. Run deno fmt to format, deno lint to check style, and deno test to run tests

B. Install ESLint and Prettier manually, then run tests with deno run

C. Only run deno run since it checks everything automatically

D. Use third-party tools outside Deno for formatting and testing

Solution

1. Step 1: Identify Deno's bundled tools for code quality

   Deno includes deno fmt for formatting, deno lint for style checking, and deno test for running tests without extra installs.

2. Step 2: Compare with other options

   Installing external tools or relying only on deno run does not cover formatting or linting automatically; third-party tools add complexity.

3. Final Answer:

   Run deno fmt to format, deno lint to check style, and deno test to run tests -> Option A

4. Quick Check:

   Use bundled fmt, lint, test for quality [OK]

Hint: Use deno fmt, lint, test for full checks [OK]

Common Mistakes:

• Ignoring lint and format commands
• Installing unnecessary external tools
• Thinking deno run covers all checks