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
Author
user-image
Syed Sibtain
System Analyst
NDJSON (Newline Delimited JSON): A file format where each line is a valid, independent JSON object, separated by a newline character (\n)

Regular JSON wraps everything in an array:

Code

[
    {"name": "Alice"},
    {"name": "Bob"}
  ]


NDJSON is one object per line, no wrapper:

Code

{"name": "Alice"}
  {"name": "Bob"}


Didn't know this existed. Turns out it's really useful for:
- Log files — each event is one line, easy to grep
- Streaming APIs — send objects as they're ready, don't wait for the full array
- Large datasets — process line by line without loading everything into memory

Also called JSONL (JSON Lines). Same thing. Claude Code uses this to send MCP messages over stdio
#json
Published
Author
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Nitturu Baba
System Analyst
Ruby hashes treat strings and symbols as different keys.
But JSON data (JWT, APIs) always comes with string keys.

Code

decoded = { "user_id" => 1 }

decoded[:user_id]   # => nil ❌
decoded["user_id"]  # => 1


This silently breaks code when Rails-style symbol access is used.

We can use HashWithIndifferentAccess which removes this mismatch:

Code

payload = HashWithIndifferentAccess.new(decoded)

payload[:user_id]   # => 1
payload["user_id"]  # => 1


You no longer care whether keys are strings or symbols. Rails params works the same way internally.

HashWithIndifferentAccess is a class provided by ActiveSupport, so it exists only in Rails, not in core Ruby. It internally normalizes all keys (by storing them as strings) while allowing access using either symbols or strings. It’s designed specifically for boundary data—like JSON responses, JWT payloads, and request params—where key formats are inconsistent. By removing the need to care about key types, it prevents subtle nil bugs without forcing changes in how the rest of the code is written, which is why Rails uses it internally for params

#Rails
Published
Author
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Satya
When two models are associated—for example, a Chat that has many Messages—you can create a message using @chat.messages.build instead of instantiating Message.new. This automatically sets the chat_id on the message, so it’s never niland the association is correctly maintained

#ActiveRecord #Rails
Published
Author
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Syed Sibtain
System Analyst
What is Framing in WebSockets?
Framing is how WebSocket data is split, structured, and transmitted over the wire. Framing is protocol-level, not app-level

WebSockets do not send raw strings or JSON directly. Instead, every message is wrapped inside WebSocket frames.

Each WebSocket frame contains:
• FIN bit – is this the final frame?
• Opcode – what type of data?
• Payload length
• Masking key (client → server)
• Payload data
Frame Types
Data frames
• Text frame → UTF-8 text (JSON, strings)
• Binary frame → raw bytes (files, protobuf)
Control frames
• PING → check if connection is alive
• PONG → response to ping
• CLOSE → graceful shutdown
#websockets #client #server
Published
Author
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Swasthik K
Cron in GitHub Actions
In GitHub Actions, you can schedule workflows using cron syntax inside the on.schedule field. It uses UTC time format.
Example:

Code

on:
  schedule:
    # Runs at 5:30 AM and 5:30 PM UTC every day
    - cron: '30 5,17 * * *'
    # Runs every 15 minutes
    - cron: '*/15 * * * *'
    # Runs every Monday at 9:00 AM UTC
    - cron: '0 9 * * 1'


Cron format:
┌───────── minute (0–59)
│ ┌─────── hour (0–23)
│ │ ┌───── day of month (1–31)
│ │ │ ┌─── month (1–12)
│ │ │ │ ┌─ day of week (0–6, Sun=0)
│ │ │ │ │
* * * * *

#GitHubActions #DevOps
Published
Author
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Swasthik K
Syntax Highlighting & Language Detection with Highlight.js

It's a lightweight JS library that automatically highlights and detects code syntax on web pages — no need for manual markup.

Installing Highlight.js

Code

pnpm add highlight.js


Detect Language & Highlight

Code

import hljs from 'highlight.js';
import 'highlight.js/styles/atom-one-dark.css';

const code = `function sum(a, b) { return a + b; }`;
const { value, language } = hljs.highlightAuto(code);

console.log(language); // e.g. "javascript"
console.log(value); // highlighted HTML


• You can pass value to your React component and render it inside a code element with the hljs class for styling.
Highlight.js automatically detects the language and highlights it — perfect when your app handles multiple code types dynamically.

#JavaScript #Frontend #HighlightJS
Published
Author
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Vaibhav Yadav
Senior System Analyst
Clean up merged Git branches easily

You can quickly delete all local branches that have already been merged into your current branch (like master or main) using a single command:


Code

git branch --merged | egrep -v "(^\*|master|main)" | xargs git branch -d


This command lists all merged branches, filters out the current and main branches, and deletes the rest safely. Perfect for keeping your local repo tidy after merging multiple feature branches.

#git #github #vcs
Published
Author
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Puneeth kumar
System Analyst
Understanding the Difference Between Regular Imports and .forRoot() in NestJS

In NestJS, modules can be imported in two main ways — but they behave differently:

1 Regular Imports
• Example imports: [ProjectsModule, UserModule]
• These are simple — they bring in the module’s exports (like services or guards).
• They don’t need any setup or configuration.
2.1 forRoot() Imports
• Example imports: [SlackModule.forRoot(dbClient)
• These are special. They let a module set itself up with configuration or dependencies (like a DB client, API key, etc.).
• They create a global instance that’s initialized once across the app.
2.2 forRootAsync()
• Used when setup depends on async config — like environment variables.
• Example :

Code

PgBossModule.forRootAsync({
  useFactory: async (config) => ({
    connectionString: config.get('DATABASE_URL'),
  }),
  inject: [ConfigService],
});


Conclusion
• Regular imports are sufficient when we just need access to a module’s services or exports.
• forRoot() is useful when a module requires initial configuration or dependencies.
• forRootAsync() is ideal when configuration depends on asynchronous operations, such as reading environment variables or fetching secrets.
#NestJS #import_module
Published
Author
user-image
Syed Sibtain
System Analyst
getBoundingClientRect() A crucial DOM method that gives us an element's position and size relative to the viewport, not the document.

Example:

Code

const rect = container.getBoundingClientRect();


What getBoundingClientRect() returns?

Code

{
  top: 100,      // Distance from viewport top to element top
  left: 200,     // Distance from viewport left to element left  
  right: 400,    // Distance from viewport left to element right
  bottom: 300,   // Distance from viewport top to element bottom
  width: 200,    // Element width
  height: 200,   // Element height
  x: 200,        // Same as left (for compatibility)
  y: 100         // Same as top (for compatibility)
}


Real Usage Example: Image Comparison Slider:

Code

// User drags the slider to compare two images
handleDrag(event) {
  const container = this.getContainer(); // The image container
  const rect = container.getBoundingClientRect();
  
  // Convert global mouse position to slider position
  const x = event.clientX - rect.left;  // Mouse X relative to container
  const percentage = this.calculatePercentage(x, rect.width);
  
  // Update slider position (0-100%)
  this.sliderPosition = percentage;
  this.updateSliderPosition(percentage);
}


Step-by-Step Breakdown:
1. User drags mouse → event.clientX = 350 (global position)
2. Get container bounds → rect.left = 200 (container starts at 200px from viewport left)
3. Calculate relative position → 350 - 200 = 150px (mouse is 150px from container's left edge)
4. Convert to percentage → 150 / 400 = 37.5% (150px out of 400px container width)
5. Update slider → Move slider to 37.5% position
getBoundingClientRect() is the bridge between global coordinates and element-relative coordinates.

#CCT1JMA0Z #stimulus
Published
Author
user-image
Syed Sibtain
System Analyst
When we rewrite git history (like squashing commits, interactive rebase), our local branch diverges from the remote branch.
A regular git push will be rejected because the histories don't match. The first option is git push --force, which overwrites the remote branch with our local version.

The Usual Approach: git push --force

Code

# DANGEROUS - can overwrite other people's work
# We do it everyday though
git push --force origin <feature-branch>


The Safer Alternative: git push --force-with-lease

Code

# SAFER - includes safety checks
git push --force-with-lease origin feature-branch


How --force-with-lease works:
• Checks if the remote branch has moved since we last fetched it.
• Only overwrites if the remote is exactly where we expect it to be.
• Fails safely if someone else has pushed commits we don't have locally.
• Prevents accidental overwrites of other people's work.
PS: Might sound simple, but helps a lot when working with bigger teams.

#git #github

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