deno lint for code quality - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to run Deno's linter on a file named app.ts.

Deno

deno [1] app.ts

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

Alint

Brun

Ctest

Dfmt

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'deno run' instead of 'deno lint'.

Trying 'deno fmt' which formats code but does not lint.

Use deno lint to check code quality and style issues in your Deno files.

2fill in blank

medium

Complete the code to lint all files in the current directory recursively.

Deno

deno lint [1]

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

A--watch

B--all

C--check

D.

Attempts:

3 left

💡 Hint

Common Mistakes

Using '--all' which is not a valid lint flag.

Using '--watch' which watches files but does not lint recursively.

The . specifies the current directory, which Deno lints recursively including all files in subfolders.

3fill in blank

hard

Fix the error in the command to lint only mod.ts and ignore warnings.

Deno

deno lint mod.ts [1]

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

A--quiet

B--ignore

C--silent

D--no-warnings

Attempts:

3 left

💡 Hint

Common Mistakes

Using '--no-warnings' which is not a valid Deno lint flag.

Using '--ignore' which is for ignoring files, not suppressing warnings.

The --quiet flag suppresses warnings and shows only errors.

4fill in blank

hard

Fill both blanks to run lint on src/ folder and fix problems automatically.

Deno

deno lint [1] [2]

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

Asrc/

B--fix

C--watch

D--unstable

Attempts:

3 left

💡 Hint

Common Mistakes

Using '--watch' instead of '--fix' for automatic fixing.

Not specifying the folder path correctly.

Use the folder path src/ and the --fix flag to auto-correct lint issues.

5fill in blank

hard

Fill all three blanks to lint lib/ folder recursively, show only errors, and use unstable features.

Deno

deno lint [1] [2] [3]

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

Alib/

B--quiet

C--unstable

D--fix

Attempts:

3 left

💡 Hint

Common Mistakes

Using '--fix' instead of '--quiet' to reduce output.

Not using the folder path to lint all files in subfolders.

Use lib/ to lint the folder (recursively by default), --quiet to show only errors, and --unstable to enable unstable lint features.

Practice

1. What is the main purpose of running deno lint on your code?

easy

A. To execute the code and show output

B. To find and report code style and potential error issues

C. To compile the code into a binary

D. To install external dependencies automatically

Solution

1. Step 1: Understand what linting means

   Linting is a process that checks code for style and possible mistakes without running it.

2. Step 2: Identify what deno lint does

   deno lint scans your code files and reports style issues or errors to improve code quality.

3. Final Answer:

   To find and report code style and potential error issues -> Option B

4. Quick Check:

   Linting = Find code issues [OK]

Hint: Lint checks code style and errors, not execution or compilation [OK]

Common Mistakes:

• Confusing lint with running or compiling code
• Thinking lint installs dependencies
• Assuming lint fixes all errors automatically

2. Which command correctly runs the linter on all files in the current folder and subfolders?

easy

A. deno lint --fix

B. deno run lint

C. deno lint .

D. deno lint --all

Solution

1. Step 1: Identify the command to lint files

   The command deno lint followed by a path runs lint on that path.

2. Step 2: Understand the meaning of '.' in commands

   Using '.' means current directory and all files inside it recursively.

3. Final Answer:

   deno lint . -> Option C

4. Quick Check:

   Lint current folder = deno lint . [OK]

Hint: Use dot (.) to lint current folder and subfolders [OK]

Common Mistakes:

• Using 'deno run lint' which is invalid
• Assuming '--all' is a valid flag for deno lint
• Confusing '--fix' as a way to run lint only

3. Given this code snippet in example.ts:

const unusedVar = 5;
console.log("Hello Deno!");

What will deno lint example.ts report?

medium

A. Error: unused variable 'unusedVar'

B. Warning: missing semicolon

C. Syntax error on line 1

D. No issues found

Solution

1. Step 1: Analyze the code for lint issues

   The variable unusedVar is declared but never used, which is a common lint warning.

2. Step 2: Understand what deno lint reports

   Deno lint reports unused variables as errors or warnings to improve code quality.

3. Final Answer:

   Error: unused variable 'unusedVar' -> Option A

4. Quick Check:

   Unused variable = lint error [OK]

Hint: Unused variables cause lint errors, check variable usage [OK]

Common Mistakes:

• Thinking no issues appear if code runs
• Confusing lint errors with syntax errors
• Expecting semicolon warnings when not configured

4. You run deno lint and get errors about unused imports. Which fix will resolve this?

medium

A. Ignore the errors and continue running the code

B. Add --fix flag to automatically remove unused imports

C. Rename the imports to different variable names

D. Remove the unused import lines from the code

Solution

1. Step 1: Understand what unused import errors mean

   Unused imports are lines importing modules or variables that are never used in the code.

2. Step 2: Identify the correct fix

   Removing those unused import lines cleans the code and fixes the lint errors. The --fix flag does not always remove imports automatically.

3. Final Answer:

   Remove the unused import lines from the code -> Option D

4. Quick Check:

   Remove unused imports to fix lint errors [OK]

Hint: Delete unused imports manually; --fix may not remove them [OK]

Common Mistakes:

• Assuming --fix always removes unused imports
• Ignoring lint errors thinking code still runs
• Renaming imports without using them

5. You want to automatically fix some lint issues in your project folder. Which command should you run?

hard

A. deno lint --fix ./

B. deno lint --auto-fix ./

C. deno lint fix ./

D. deno lint --correct ./

Solution

1. Step 1: Recall the flag for automatic fixing in deno lint

   The correct flag to fix some lint issues automatically is --fix.

2. Step 2: Confirm the command syntax

   The command deno lint --fix ./ runs lint on the current folder and applies automatic fixes where possible.

3. Final Answer:

   deno lint --fix ./ -> Option A

4. Quick Check:

   Use --fix flag to auto-correct lint issues [OK]

Hint: Use --fix flag with deno lint to auto-correct issues [OK]

Common Mistakes:

• Using incorrect flags like --auto-fix or --correct
• Typing 'deno lint fix' without dashes
• Not specifying the folder or file to lint