deno fmt for code formatting

Introduction

deno fmt helps you keep your code neat and easy to read by fixing spacing and indentation automatically.

When you want all your Deno code files to look consistent.

Before sharing your code with others to make it clean.

After writing code quickly and you want to tidy it up.

To avoid style arguments in a team by using a standard format.

When you want to quickly fix formatting mistakes without manual edits.

Syntax

Deno

deno fmt [options] [files...]

You can run it without arguments to format all supported files in the current folder.

Use file paths or glob patterns to format specific files.

Examples

Formats all supported files in the current directory and subdirectories.

Deno

deno fmt

Formats the file mod.ts and all TypeScript files in the utils folder.

Deno

deno fmt mod.ts utils/*.ts

Checks if files are formatted without changing them. Useful for CI or pre-commit checks.

Deno

deno fmt --check

Sample Program

This example shows a small unformatted TypeScript function. Running deno fmt fixes spacing, adds missing semicolons, and formats the code nicely.

Deno

/* Unformatted code example */
function greet (name:string){console.log("Hello, " +name)}
greet("Deno")

// Run in terminal:
deno fmt

/* After formatting, code looks like: */
function greet(name: string) {
  console.log("Hello, " + name);
}

greet("Deno");

Important Notes

deno fmt supports TypeScript, JavaScript, JSON, and more file types.

You can configure formatting rules with a deno.json file if needed.

Running deno fmt is safe and won't change your code logic, only style.

Summary

deno fmt automatically formats your code for readability and consistency.

Use it often to keep your project clean and avoid style debates.

It works on many file types and can check formatting without changing files.

Practice

1. What is the main purpose of the deno fmt command?

easy

A. To install third-party modules

B. To run your Deno program

C. To automatically format your code for better readability and consistency

D. To check for security vulnerabilities in your code

Solution

1. Step 1: Understand the role of deno fmt

   deno fmt is designed to format code automatically, making it easier to read and consistent across files.

2. Step 2: Differentiate from other commands

   Running programs, installing modules, or security checks are done by other commands like deno run, deno install, or deno lint.

3. Final Answer:

   To automatically format your code for better readability and consistency -> Option C

4. Quick Check:

   deno fmt formats code [OK]

Hint: Remember: fmt means format code automatically [OK]

Common Mistakes:

• Confusing fmt with run or install commands
• Thinking fmt checks code errors instead of formatting
• Assuming fmt modifies program logic

2. Which of the following is the correct way to run deno fmt on all supported files in your project?

easy

A. deno fmt

B. deno fmt install

C. deno fmt run

D. deno fmt --check

Solution

1. Step 1: Identify the basic command to format files

   Running deno fmt without extra flags formats all supported files in the current directory and subdirectories.

2. Step 2: Understand other options

   --check only checks formatting without changing files; run and install are unrelated commands.

3. Final Answer:

   deno fmt -> Option A

4. Quick Check:

   Basic command to format = deno fmt [OK]

Hint: Use just 'deno fmt' to format all files quickly [OK]

Common Mistakes:

• Adding unnecessary flags like run or install
• Using --check when wanting to format files
• Confusing fmt with other Deno commands

3. Given this unformatted TypeScript code in example.ts:

function greet ( name:string ){console.log( "Hello, " +name );}

What will be the output in example.ts after running deno fmt?

medium

A. function greet ( name:string ){console.log( "Hello, " +name );}

B. function greet(name: string) {
console.log("Hello, " + name);
}

C. function greet(name:string){console.log("Hello,"+name);}

D. function greet(name: string) {console.log("Hello," + name);}

Solution

1. Step 1: Understand what deno fmt does to code style

   deno fmt adds spaces after commas, spaces around operators, and proper indentation and line breaks for readability.

2. Step 2: Compare options with expected formatting

   function greet(name: string) { console.log("Hello, " + name); } shows proper spacing after parameters, braces on new lines, and indentation inside the function, matching deno fmt style.

3. Final Answer:

   function greet(name: string) { console.log("Hello, " + name); } -> Option B

4. Quick Check:

   deno fmt adds spaces and indentation [OK]

Hint: Look for spaces after colons and proper indentation [OK]

Common Mistakes:

• Ignoring spaces after colons and commas
• Not indenting inside function blocks
• Keeping all code on one line

4. You run deno fmt --check on your project and get an error saying some files are not formatted. What should you do to fix this?

medium

A. Run deno fmt without flags to format the files automatically

B. Ignore the error because it does not affect code execution

C. Delete the files that are not formatted

D. Run deno run to fix formatting issues

Solution

1. Step 1: Understand what deno fmt --check does

   This command checks if files are formatted but does not change them.

2. Step 2: Fix formatting issues

   To fix formatting, run deno fmt without flags to automatically format all files.

3. Final Answer:

   Run deno fmt without flags to format the files automatically -> Option A

4. Quick Check:

   Use deno fmt to fix formatting [OK]

Hint: Use deno fmt (no flags) to fix formatting errors [OK]

Common Mistakes:

• Ignoring formatting errors thinking they don't matter
• Trying to fix formatting by running code
• Deleting files instead of formatting

5. You want to ensure your project code is always formatted before committing to Git. Which command can you add to your Git pre-commit hook to automatically format all files using Deno?

hard

A. deno run

B. deno install

C. deno lint

D. deno fmt

Solution

1. Step 1: Identify the command that formats code automatically

   deno fmt formats all supported files, making it ideal for pre-commit hooks to keep code clean.

2. Step 2: Understand other commands' purposes

   deno run executes scripts, deno lint checks code style but does not fix formatting, and deno install installs scripts.

3. Final Answer:

   deno fmt -> Option D

4. Quick Check:

   Pre-commit formatting uses deno fmt [OK]

Hint: Use deno fmt in pre-commit hooks to auto-format code [OK]

Common Mistakes:

• Using deno run or deno lint instead of fmt
• Thinking lint fixes formatting automatically
• Not automating formatting before commits