js-core

This repository is a from-scratch, interview-grade deep dive into JavaScript. It focuses on how JS actually works under the hood: execution model, async behavior, DOM mechanics, and performance patterns. Everything here is written to build first-principles clarity.

Why this repo exists

Most JS resources teach what to write. This repo teaches why it works.

If you:

Know JavaScript syntax but feel shaky about internals
Want to reason about performance instead of guessing
Are preparing for SDE-2 / Senior-level interviews
Want to build a rock-solid mental model before touching frameworks

→ this repo is for you.

What you will learn

1. JavaScript Core

Data types & coercion (truth tables, edge cases)
Execution context & call stack
Scope chain, lexical environment
var vs let vs const
Hoisting (real behavior, not myths)

2. Functions (Deep Dive)

Function declarations vs expressions
Arrow functions (design trade-offs)
this binding (call/apply/bind)
Closures (how & why they exist)
Pure vs impure functions

3. Asynchronous JavaScript

Event loop (step-by-step)
Microtasks vs macrotasks
Promises (states, chaining, error flow)
async/await (what it compiles to mentally)
Concurrency vs parallelism

4. DOM & Browser Internals

What the DOM actually is
Event propagation (capture → target → bubble)
Event delegation (why it matters)
Reflow vs repaint
Browser rendering pipeline

5. Performance Patterns

Debouncing vs throttling
Avoiding unnecessary reflows
Memory leaks (common JS mistakes)
Time & space complexity thinking in JS

Repo Structure

js-core/
│
├── 01-basics/          # Language fundamentals & execution model
├── 02-functions/       # this, closures, bindings, arrow functions
├── 03-prototypal-js/   # Prototype Chain, Prototypal Inheritance vs. Class-based syntax, and Shadowing.
├── 04-async-architecture/        # event loop, promises, async/await
├── 05-dom/             # DOM, events, rendering
├── 06-performance/     # optimization patterns && polyfils
├── notes/           # concise interview-ready notes
└── README.md

Folder names are conceptual, not random. Each builds on the previous one.

How to use this repo

Recommended order:

Read the notes
Run the examples
Predict output before executing
Break things intentionally

This repo rewards thinking, not memorization.

Philosophy

No frameworks
No magic
No copy-paste learning

Every concept is explained until it becomes obvious.

If you can explain it simply, you truly understand it.

Who this is for

Intermediate JS developers leveling up
Interview prep (SDE-2 / Senior Frontend / Fullstack)
Backend engineers who want real JS mastery
Anyone tired of shallow tutorials

Status

🚧 Actively growing

Concepts are added only after being fully reasoned and verified.

License

MIT — use it, break it, improve it.

Final Note

If this repo makes JavaScript feel predictable instead of magical, it has done its job.

Happy breaking things 🚀

bikashrajkhowa-i12/js-core