Lock files for dependency integrity in Deno - Step-by-Step Execution

Concept Flow - Lock files for dependency integrity

Start: Run Deno with dependencies

↓

Check for lock file

↓

Verify hashes

↓

Match?

No|↓

Error: Dependency changed

↓

Stop

Deno checks if a lock file exists to verify dependency hashes. If missing, it creates one. If hashes mismatch, it stops to keep dependencies safe.

Execution Sample

Deno

deno run --lock=lock.json --lock-write mod.ts
import { serve } from "https://deno.land/std/http/server.ts";
serve(() => new Response("Hello"));

This runs a Deno script using a lock file to ensure dependencies are exactly as recorded.

Execution Table

Step	Action	Lock File Exists?	Dependency Hash Check	Result
1	Start running script	Yes	Check hashes in lock.json	Proceed if all match
2	Dependency hash matches	Yes	Hashes match	Load dependency
3	Run script	Yes	All dependencies verified	Script runs successfully
4	Modify dependency externally	Yes	Hashes mismatch	Error: Dependency changed, stop execution
5	Run with no lock file	No	No lock file found	Create lock.json with current hashes
6	Run again with new lock file	Yes	Hashes match new lock.json	Script runs successfully

💡 Execution stops if dependency hashes do not match lock file to protect integrity.

Variable Tracker

Variable	Start	After Step 1	After Step 4	After Step 5	Final
lockFileExists	Unknown	Yes	Yes	Yes	Yes
dependencyHashesMatch	Unknown	True	False	N/A	True
scriptRuns	No	No	No	Yes	Yes

Key Moments - 2 Insights

Why does Deno stop running the script when hashes don't match the lock file?

Deno stops to prevent running code with unexpected or changed dependencies, ensuring security and consistency as shown in execution_table step 4.

What happens if there is no lock file when running a Deno script?

Deno creates a new lock file with current dependency hashes to track integrity, as seen in execution_table step 5.

Visual Quiz - 3 Questions

Look at the execution_table, at which step does Deno detect a dependency hash mismatch?

A Step 2

B Step 4

C Step 5

D Step 6

💡 Hint

Check the 'Dependency Hash Check' column for mismatch indication.

According to variable_tracker, what is the value of 'lockFileExists' after step 5?

A Yes

B Unknown

C No

D False

💡 Hint

Look at the 'lockFileExists' row under 'After Step 5' column.

If the lock file is missing, what does Deno do according to the execution flow?

A Stops execution with error

B Ignores dependencies

C Creates a new lock file with current hashes

D Runs script without verification

💡 Hint

Refer to the decision branch where 'Lock File Exists?' is No.

Concept Snapshot

Deno uses lock files to keep dependencies safe.
Run with --lock=lock.json to check hashes.
Use --lock-write to create/update lock files.
If hashes differ, Deno stops to avoid risks.
Lock files ensure consistent, secure runs.

Full Transcript

When you run a Deno script with a lock file, Deno first checks if the lock file exists. If it does, it compares the hashes of all dependencies with those saved in the lock file. If all hashes match, the script runs safely. If any hash differs, Deno stops running to protect you from unexpected changes. If no lock file exists, Deno creates one with the current dependency hashes. This process ensures your code always uses the exact same dependencies, keeping your project secure and consistent.

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