Lock files for dependency integrity in Deno - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of a lock file in Deno?

A lock file in Deno records the exact versions and hashes of dependencies used. It ensures that every time the project runs, the same trusted versions are used, preventing unexpected changes.

beginner

How do you create a lock file in Deno?

You create a lock file by running your Deno command with the flag --lock=lock.json and --lock-write. This writes the current dependencies and their hashes into lock.json.

intermediate

What happens if a dependency changes but the lock file does not match in Deno?

Deno will refuse to run the program and show an error. This protects you from running code with unexpected or unverified dependencies.

beginner

Why is it important to commit the lock file to version control?

Committing the lock file ensures all team members and deployment environments use the exact same dependency versions, avoiding bugs caused by different versions.

intermediate

Which command flags are used together to enforce lock file usage in Deno?

Use --lock=lock.json to specify the lock file and --lock-write to create or update it. To enforce usage without updating, use --lock=lock.json without --lock-write.

What does the Deno lock file store?

A User environment settings

B Exact versions and hashes of dependencies

C Only the names of dependencies

D Compiled JavaScript code

The lock file stores exact versions and cryptographic hashes of dependencies to ensure integrity.

Which flag creates or updates the lock file in Deno?

A --allow-net

B --reload

C --unstable

D --lock-write

The --lock-write flag tells Deno to write or update the lock file.

What happens if a dependency's hash does not match the lock file during execution?

A Deno ignores the mismatch

B Deno updates the lock file automatically

C Deno throws an error and stops

D Deno runs the code anyway

Deno stops execution to protect against untrusted or changed dependencies.

Why should you commit the lock file to your git repository?

A To ensure consistent dependencies across all environments

B To speed up git operations

C To store user passwords

D To enable auto-updates of dependencies

Committing the lock file ensures everyone uses the same dependency versions.

How do you enforce using the lock file without updating it?

A Use --lock=lock.json without --lock-write

B Use --lock-write only

C Use --reload

D Use --unstable

Using --lock=lock.json without --lock-write enforces the lock file without changing it.

Explain what a lock file is in Deno and why it is important for dependency integrity.

Think about how you keep a recipe exactly the same every time you cook.

Describe the steps to create and use a lock file in a Deno project.

Consider how you save and share a shopping list to keep everyone buying the same items.

Practice

1. What is the main purpose of a lock file in a Deno project?

easy

A. To list all available Deno commands

B. To speed up the execution of Deno scripts

C. To save exact versions of dependencies for consistent builds

D. To store environment variables securely

Solution

1. Step 1: Understand what a lock file does

   A lock file records the exact versions and hashes of dependencies used in a project to ensure consistency.

2. Step 2: Identify the purpose in Deno context

   In Deno, the lock file prevents unexpected changes by locking dependency versions during installs and runs.

3. Final Answer:

   To save exact versions of dependencies for consistent builds -> Option C

4. Quick Check:

   Lock file = exact dependency versions [OK]

Hint: Lock files keep dependencies stable and consistent [OK]

Common Mistakes:

• Thinking lock files speed up script execution
• Confusing lock files with environment variable storage
• Assuming lock files list commands

2. Which Deno command option is used to create or update a lock file?

easy

A. --unstable

B. --lock

C. --reload

D. --lock-write

Solution

1. Step 1: Identify command options related to lock files

   --lock is used to specify a lock file to use, but does not create or update it.

2. Step 2: Understand which option writes the lock file

   --lock-write tells Deno to create or update the lock file with current dependencies.

3. Final Answer:

   --lock-write -> Option D

4. Quick Check:

   Update lock file = --lock-write [OK]

Hint: Use --lock-write to create or update lock files [OK]

Common Mistakes:

• Using --lock alone to update lock files
• Confusing --reload with lock file creation
• Thinking --unstable manages lock files

3. Given the command deno run --lock=lock.json --unstable app.ts, what will happen if lock.json is missing?

medium

A. Deno will throw an error and refuse to run

B. Deno will create a new lock.json automatically

C. Deno will run the script but ignore dependencies

D. Deno will run the script without checking the lock file

Solution

1. Step 1: Understand the --lock option behavior

   Using --lock requires the specified lock file to exist; otherwise, Deno refuses to run to ensure integrity.

2. Step 2: Check what happens if the lock file is missing

   If lock.json is missing, Deno throws an error and stops execution to prevent unverified dependencies.

3. Final Answer:

   Deno will throw an error and refuse to run -> Option A

4. Quick Check:

   Missing lock file + --lock = error [OK]

Hint: --lock requires existing file; missing file causes error [OK]

Common Mistakes:

• Assuming Deno creates lock file automatically
• Thinking Deno ignores missing lock files
• Confusing --lock with --lock-write behavior

4. You run deno run --lock=lock.json app.ts but get an error about a missing lock file. What is the best way to fix this?

medium

A. Delete the lock.json file and rerun the command

B. Run deno run --lock=lock.json --lock-write app.ts to create the lock file

C. Remove the --lock option from the command

D. Run deno cache app.ts without any lock options

Solution

1. Step 1: Identify cause of error

   The error occurs because the specified lock file does not exist yet.

2. Step 2: Use correct command to create lock file

   Adding --lock-write creates or updates the lock file while running the script.

3. Final Answer:

   Run deno run --lock=lock.json --lock-write app.ts to create the lock file -> Option B

4. Quick Check:

   Create lock file with --lock-write [OK]

Hint: Add --lock-write to create missing lock file [OK]

Common Mistakes:

• Deleting lock file instead of creating it
• Removing --lock option and losing integrity
• Running cache without lock options

5. You want to ensure your team uses the exact same dependencies in production and development. Which practice with lock files is best?

hard

A. Commit the lock file to version control and use --lock on all runs

B. Generate a new lock file on each developer machine separately

C. Ignore the lock file and rely on latest versions always

D. Use --lock-write only in production, not in development

Solution

1. Step 1: Understand team consistency needs

   To keep dependencies consistent, everyone must use the same locked versions.

2. Step 2: Identify best lock file usage practice

   Committing the lock file to version control and using --lock ensures all environments use identical dependencies.

3. Final Answer:

   Commit the lock file to version control and use --lock on all runs -> Option A

4. Quick Check:

   Share lock file + use --lock = consistent deps [OK]

Hint: Commit lock file and use --lock for team consistency [OK]

Common Mistakes:

• Generating separate lock files causing version drift
• Ignoring lock files and risking inconsistent builds
• Using --lock-write only in production causing mismatch