TILs - Fueling Curiosity, One Insight at a Time

At Codemancers, we believe every day is an opportunity to grow. This section is where our team shares bite-sized discoveries, technical breakthroughs and fascinating nuggets of wisdom we've stumbled upon in our work.

Published: May 28, 2025
Author: Sudeep Hipparge

JavaScript: Object.groupBy()

Grouping data used to be messy — relying on Array.reduce() with verbose logic. But JavaScript's new Object.groupBy() method has made things incredibly elegant and easy!

With just one line, you can group array items based on any property.
It’s clean, readable, and production-friendly.

📌 Example:

Code

const products = [
  { name: "T-shirt", category: "clothes", price: 50 },
  { name: "Apple", category: "food", price: 5 },
  { name: "Shoes", category: "clothes", price: 35 },
  { name: "Orange", category: "food", price: 7.5 },
  { name: "Blueberry", category: "food", price: 4.5 }
];

const grouped = Object.groupBy(products, product => product.category);

console.log(grouped);

💡 Output:

Code

{
  clothes: [
    { name: "T-shirt", category: "clothes", price: 50 },
    { name: "Shoes", category: "clothes", price: 35 }
  ],
  food: [
    { name: "Apple", category: "food", price: 5 },
    { name: "Orange", category: "food", price: 7.5 },
    { name: "Blueberry", category: "food", price: 4.5 }
  ]
}

✅ Cleaner. ✅ Less boilerplate. ✅ Much easier to read.

#CCT1JMA0Z #WebDevelopment

Published: May 28, 2025
Author: Vaibhav Yadav
Senior System Analyst

Using Makefile for tedious commands

A Makefile can be used to automate a commands, simplifying the execution process. Here’s a concise example:

Code

.PHONY: run-script

# Target to run a long command
run-script:
    @echo "Running a long command..."
    sleep 5  # Simulate a long-running command
    @echo "Command completed."

Running the Makefile
1. Create a Makefile: Save the above content as Makefile in your project directory.
2. Run Make: In your terminal, navigate to the project directory and execute:

Code

make run-script

Benefits
• Simplicity: Easily run a long command without remembering the syntax.
• Automation: Reduces manual effort and potential errors.
#cli #automation #makefile #commands

Published: May 26, 2025
Author: Sudeep Hipparge

💡 Why is [] == ![] true in JavaScript?

It all comes down to type coercion and how JavaScript evaluates expressions using the == (abstract equality) operator.

Here’s the breakdown:
![] evaluates to false because an empty array is truthy, and the ! operator negates it.
So the expression becomes: [] == false
When comparing an object (like[]) to a boolean with==, JavaScript converts both sides to numbers:
+[] → 0
+false → 0
So:

Code

[] == ![]  
=> [] == false  
=> +[] == +false  
=> 0 == 0  
=> true

✅ Hence, [] == ![] evaluates to true.

#CCT1JMA0Z

Published: May 24, 2025
Author: Adithya Hebbar
System Analyst

How Dependency Injection Works in NestJS

NestJS uses Dependency Injection (DI) to manage the creation and lifecycle of classes like services, repositories, and providers. It leverages TypeScript's metadata to resolve dependencies automatically.

🚀 How It Works:

• Declare Providers: Services and other classes are marked with @Injectable() to make them available for dependency injection. They are then registered as providers in a module.

Code

// user.service.ts
@Injectable()
export class UserService {
  getUsers() {
    return ['Alice', 'Bob'];
  }
}

• Register Providers in a Module

Code

// user.module.ts
@Module({
  controllers: [UserController],
  providers: [UserService],
})
export class UserModule {}

• Use the Service via Constructor Injection

Code

// user.controller.ts
@Controller('users')
export class UserController {
  constructor(private readonly userService: UserService) {}

  @Get()
  findAll() {
    return this.userService.getUsers();
  }
}

NestJS reads the constructor types and injects the required instances for you. No manual instantiation needed!

✅ Benefits:
• Decouples components
• Simplifies testing with mocks
• Promotes cleaner, modular code

#nestjs #dependencyinjection #typescript

Published: May 23, 2025
Author: Sudeep Hipparge

How to Revoke and Amend the Most Recent Git Commit Message.
To undo the most recent commit, unstage the changes, and update the commit message, follow these steps:

1. Revoke the latest commit and unstage the changes.
git reset HEAD~1

2. Stage the changes again.
git add .

3. Create a new commit with the updated message
git commit -m "New commit message"
(If you just want to change the previous commit message) - git commit --amend

4. Force-push the new commit to the remote repository
git push origin <branch-name> --force

> ⚠️ Use --force cautiously, especially on shared branches, as it rewrites history.

Published: May 20, 2025
Author: Nived Hari
System Analyst

pgvector provides native support for vector similarity search in PostgreSQL. It supports three types of distance metrics, each useful depending on the use case:
• <=> Cosine distance – Measures the angle between two vectors (ignores magnitude). Great for comparing meaning in text (e.g., NLP). Smaller angle = more similar.
• <#> L2 (Euclidean distance) – Measures the straight-line distance between two vectors. Takes both direction and size into account. Good when actual value differences matter (like in image or audio data).
• <-> Inner product – Measures how much two vectors point in the same direction and how large they are. If vectors are normalized (length = 1), it works like cosine similarity. Great for ranking similarity when vectors are preprocessed.

#pgvector #PostgreSQL #VectorSearch #Embeddings

Published: May 20, 2025
Author: Puneeth kumar
System Analyst

ClickHouse DB

It is a column-oriented database management system designed for online analytical processing (OLAP). It's optimised for real-time analytics on large volumes of data and is known for being fast, highly scalable, and efficient for read-heavy workloads like metrics, logs, events, and other analytical data.

Key features are -
1. Columnar storage : Stores data by columns instead of rows, enabling efficient compression and faster reads.
2. Works super fast : Designed to process billions of rows per second per server.
3. SQL-compatible.
4. Materialized views : For real-time aggregation and data transformation.
#databases #click_house_db #analytics

Published: May 7, 2025
Author: Puneeth kumar
System Analyst

Validating date and time field in Rails

validates_timeliness gem helps us to check if a date or time field is valid and meets certain conditions — like being in the past, in the future, or within a specific range. It can do following things.
1. Check if a date is valid (e.g., "2025-02-30" is not a valid date).
2. Make sure a date is before or after a certain time as needed.
3. Restrict a field to only accept dates, times or datetimes.
4. Works well with user input in different formats.
For example :

Code

class Event < ApplicationRecord
  validates_timeliness :start_time, on_or_after: :now, type: :datetime
end

This makes sure start_time is not in the past.

#CU6U0R822 #date_time_validation

Published: May 5, 2025
Author: Mohammad hussain
System Analyst

friendly_id is a Rails gem that lets you use secure, human-readable slugs instead of record IDs in URLs.
https://github.com/norman/friendly_id
it updates the url
from this :

Code

https://localhost:3000/employer/job_posts/2/job_applications/new

to this:

Code

https://localhost:3000/employer/job_posts/frontend-developer-37b70ea4-761e-4369-832e-f5b373f7f00b/job_applications/new

#CU6U0R822

Published: Apr 29, 2025
Author: Syed Sibtain
System Analyst

rails_representation_url in Rails is used to generate a URL for a variant of an Active Storage image, not the original blob. It's especially useful when we want to apply transformations like resizing or converting image formats on-the-fly.

Code

rails_representation_url(
  image.variant(resize_to_limit: [300, 300], saver: { quality: 80 }, format: :webp).processed,
  only_path: true
)

• image.variant(...) creates a variant of the image, resizing it to a maximum of 300x300 pixels, converting it to WebP format, and reducing its quality for optimization.
• .processed ensures the variant is actually processed before generating the URL.
• rails_representation_url(...) then generates the URL for this transformed version.
• only_path: true returns a relative path (instead of a full URL), which is often preferred in views or frontend routing.
This is a great way to deliver performance-optimized images for the UI

#rubyonrails

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