Lock files for dependency integrity in Deno - Mini Project: Build & Apply

Lock files for dependency integrity

📖 Scenario: You are building a small Deno project that uses external libraries. To make sure your project always uses the exact same versions of these libraries, you will create and use a lock file.

🎯 Goal: Create a Deno project that imports a library, generate a lock file to lock dependencies, and configure Deno to use the lock file when running the project.

📋 What You'll Learn

Create a Deno script that imports the colors module from https://deno.land/std@0.203.0/fmt/colors.ts

Create a lock file named lock.json to lock the dependencies

Configure the Deno run command to use the lock file and ensure it is checked

Modify the script to print a colored message using the imported module

💡 Why This Matters

🌍 Real World

Lock files help keep your project dependencies stable and secure by preventing unexpected changes when others run your code or when you deploy.

💼 Career

Understanding how to use lock files is important for software developers to maintain reliable builds and avoid bugs caused by changing dependencies.

1

Create a Deno script importing the colors module

Create a file named mod.ts and write a line to import green from https://deno.land/std@0.203.0/fmt/colors.ts.

Deno

# Import green from the colors module
# Your code here

Hint

Use the import statement with curly braces to import green from the exact URL.

2

Add a message variable to use the green color function

In mod.ts, create a constant called message and assign it the result of calling green with the string "Hello, Deno!".

Deno

import { green } from "https://deno.land/std@0.203.0/fmt/colors.ts";

# Create a constant message using green("Hello, Deno!")
# Your code here

Hint

Use const message = green("Hello, Deno!") to create the colored message.

3

Generate a lock file for dependencies

Run the Deno command to cache dependencies and generate a lock file named lock.json for your project.

Deno

import { green } from "https://deno.land/std@0.203.0/fmt/colors.ts";

const message = green("Hello, Deno!");

# Run the command to cache dependencies and create lock.json
# Your code here

Hint

Use deno cache --lock=lock.json --lock-write mod.ts in your terminal to generate the lock file.

4

Run the script using the lock file to ensure dependency integrity

Add a line to mod.ts to print the message variable. Then run the script with Deno using the --lock=lock.json and --lock-check flags to enforce the lock file.

Deno

import { green } from "https://deno.land/std@0.203.0/fmt/colors.ts";

const message = green("Hello, Deno!");

# Add a line to print the message
# Your code here

// Run in terminal:
// deno run --lock=lock.json --lock-check mod.ts

Hint

Use console.log(message) to print the colored message. Run with deno run --lock=lock.json --lock-check mod.ts to use the lock file.

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