Lock files for dependency integrity in Deno

Introduction

Lock files keep track of exact versions of code your project uses. They help make sure your project works the same way every time you run it.

When you want to share your Deno project with others and ensure they use the same dependencies.

When you want to avoid unexpected bugs caused by updated dependencies.

When deploying your Deno app to production to keep it stable.

When working in a team to keep everyone's environment consistent.

When you want to audit or review the exact code your project depends on.

Syntax

Deno

deno cache --lock=lock.json --lock-write main.ts

deno run --lock=lock.json main.ts

The --lock=lock.json option tells Deno to use the lock file named lock.json.

The --lock-write option creates or updates the lock file with the exact versions of dependencies.

Examples

This command downloads dependencies and writes their exact versions to lock.json.

Deno

deno cache --lock=lock.json --lock-write main.ts

This runs your program using the locked dependencies from lock.json, ensuring consistency.

Deno

deno run --lock=lock.json main.ts

If your project uses unstable Deno features, you can combine --unstable with the lock file option.

Deno

deno run --lock=lock.json --unstable main.ts

Sample Program

This simple Deno server imports a specific version of the standard HTTP server module. Using a lock file ensures this exact version is used every time.

Deno

// main.ts
import { serve } from "https://deno.land/std@0.203.0/http/server.ts";

serve(() => new Response("Hello from Deno with locked dependencies!"));

Important Notes

Always commit your lock.json file to version control so others use the same dependencies.

If you update dependencies, run deno cache --lock=lock.json --lock-write again to update the lock file.

Lock files improve security by preventing unexpected code changes from dependencies.

Summary

Lock files save exact versions of dependencies to keep your project stable.

Use --lock and --lock-write options with Deno commands to manage lock files.

Always share your lock file with your team or in production for consistent results.

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