Programming language

JavaScript Basic to Advance

This course is designed to take you on a comprehensive journey into the world of JavaScript, from its foundational principles to advanced concepts. We'll start by exploring the language's core syntax, data types, and control flow, helping you build a solid understanding of how JavaScript works.

Beginner865106 lessonsFree coursejavascript

JavaScript is the language most engineers think they know. Then they take a FAANG interview and discover the gap between "I use JavaScript every day" and "I can answer a senior interview question about closures, prototypes, the event loop, or memory under pressure."

That gap is what this course closes.

The seven engineers who built AlgoInsight have collectively been rejected by FAANG companies 58 times before they got their offers. Today they work at Google, Meta, Amazon, Microsoft, Apple, and Netflix — building products you use. They built this JavaScript course because the gap between "JavaScript tutorial" and "JavaScript at FAANG-scale interview depth" was nowhere being filled honestly.

This is JavaScript taught by people who've used it to ship production code at Microsoft on VS Code, Netflix on streaming data pipelines, and Google on distributed systems clients. Every lesson is grounded in real-world context. The closures section isn't theory — it's the closure bug Olena debugged at Zalando that taught her how scope chains actually work. The prototype chapter isn't a diagram — it's the way Nikhil thinks about prototype lookups when he's reading library code at Google.

You'll learn:

• JavaScript fundamentals taught from the engineer's perspective, not the tutorial perspective. Variables, types, scope, and execution context as senior engineers actually reason about them.
• The hard parts done properly. Closures, prototypes, this, the event loop, async patterns, modules — covered at the depth FAANG interviews demand, not the depth blog posts stop at.
• JavaScript at scale. What happens in production when JavaScript meets real workloads. Memory characteristics, performance patterns, the V8 optimization model.
• Interview-specific framing. Each major topic ends with an Interview Lens — the canonical questions you'll face, the answers that separate junior from senior, and the production stories that make your answers credible.

Each lesson is written by a founder whose career uses this material daily. You're not learning from a content team. You're learning from the engineers themselves.

Modules include: language fundamentals, scope and closures, prototypes and inheritance, this binding, the event loop, async patterns, modern ES features, modules, JavaScript memory, V8 performance, browser APIs, Node.js fundamentals, and interview synthesis.

This is the JavaScript course built for the engineer who wants to clear a serious interview — not the engineer who wants another tutorial.

Course outline

Module 1: The Story of JavaScript

The Story of JavaScript

• How JavaScript Was Born 5 min read
• Birth of ECMAScript 5 min read
• JavaScript Leaves the Browser 5 min read
• Modern JavaScript: The ES6+ Era 5 min read

Module 2: Values, Types, and Coercion

Values, Types, and Coercion

• Values and Types: The Foundation 5 min read
• Strings and Template Literals 5 min read
• Numbers, BigInt, and NaN 5 min read
• Booleans and the Truthy/Falsy Trap 5 min read
• null and undefined 5 min read
• Type Coercion: Implicit and Explicit 5 min read
• Equality: == vs === 5 min read
• Interview Lens: Type Coercion 5 min read

Module 3: Variables, Scope, and Hoisting

Variables, Scope, and Hoisting

• var, let, and const 5 min read
• Scope: Global, Function, Block 5 min read
• Block vs Function Scope in Practice 5 min read
• Hoisting Explained 5 min read
• The Temporal Dead Zone 5 min read
• Interview Lens: Scope and Hoisting 5 min read

Module 4: Control Flow and Iteration

Control Flow and Iteration

• Conditionals: if, else, ternary 5 min read
• The switch Statement 5 min read
• Loops: for, while, do-while 5 min read
• Array Iteration: forEach, for...of, for...in 5 min read
• break, continue, and Loop Control 5 min read
• Interview Lens: Control Flow Patterns 5 min read

Module 5: Functions Deep Dive

Functions Deep Dive

• What Is a Function? 5 min read
• Function Declarations vs Expressions 5 min read
• Arrow Functions 5 min read
• Parameters: Defaults, Rest, Destructuring 5 min read
• Return Values and Pure Functions 5 min read
• Higher-Order Functions 5 min read
• First-Class Functions 5 min read
• Interview Lens: Functions 5 min read

Module 6: Closures and the Execution Model

Closures and the Execution Model

• Execution Context 5 min read
• Lexical Scope Revisited 5 min read
• Closures Explained 5 min read
• Closures for Private State 5 min read
• Memoization with Closures 5 min read
• Common Closure Mistakes and Memory Concerns 5 min read
• Interview Lens: Closures 5 min read

Module 7: Objects and Prototypes

Objects and Prototypes

• Objects: The Foundation 5 min read
• Property Access, Mutation, and Deletion 5 min read
• Object Methods and Shorthand Syntax 5 min read
• Iterating Over Objects 5 min read
• The Prototype Chain 5 min read
• Object.create and Prototypal Inheritance 5 min read
• Property Descriptors and Object.freeze 5 min read
• Interview Lens: Objects and Prototypes 5 min read

Module 8: this, Classes, and Inheritance

this, Classes, and Inheritance

• The `this` Keyword 5 min read
• Classes: Syntactic Sugar Over Prototypes 5 min read
• Class Methods, Constructors, and Fields 5 min read
• Inheritance with extends and super 5 min read
• Static Methods, Private Fields, Modern Class Features 5 min read
• Composition vs Inheritance 5 min read
• Interview Lens: this, Classes, and OO Patterns 5 min read

Module 9: Async JavaScript

Async JavaScript

• Why JavaScript Is Single-Threaded 5 min read
• The Event Loop, Visually 5 min read
• Callbacks: The Original Async Pattern 5 min read
• Promises, From Scratch 5 min read
• Error Handling in Promises 5 min read
• async/await: Promises in Disguise 5 min read
• Error Handling with async/await 5 min read
• Combining Promises: all, race, allSettled, any 5 min read
• The Microtask Queue, Deeply 5 min read
• Async Iteration and Generators 5 min read
• Interview Lens: The Event Loop Question 5 min read
• Interview Lens: Promise and async/await Patterns 5 min read

Module 10: Modern JavaScript (ES6+)

Modern JavaScript (ES6+)

• Destructuring: Objects and Arrays 5 min read
• Spread and Rest Operators 5 min read
• Optional Chaining and Nullish Coalescing 5 min read
• Map and Set 5 min read
• Symbols and Well-Known Symbols 5 min read
• Strict Mode and Top-Level await 5 min read
• Interview Lens: Modern JavaScript Patterns 5 min read

Module 11: Modules and the Ecosystem

Modules and the Ecosystem - Olena Marchenko - 7 Topics

• Why Modules Exist 5 min read
• ES Module Syntax: import and export 5 min read
• Default Exports vs Named Exports 5 min read
• Re-exports and Module Composition 5 min read
• CommonJS and the require/module.exports World 5 min read
• npm, package.json, and the Module Ecosystem 5 min read
• Interview Lens: Module System Questions 5 min read

Module 12: Browser, DOM, and Web APIs

Olena Marchenko (hybrid voice — light founder presence) — 7 Topics

• The Browser as a JavaScript Environment 5 min read
• DOM Fundamentals: Selecting and Reading 5 min read
• DOM Mutation: Creating, Updating, Removing 5 min read
• Events and Event Handling 5 min read
• fetch and the Modern HTTP API 5 min read
• Storage, Timers, and Other Browser APIs 5 min read
• Interview Lens: Browser and DOM Questions 5 min read

Module 13: JavaScript Engine Internals and Performance

JavaScript Engine Internals and Performance - Nikhil Joshi + Emeka Okafor — 7 Topics

• Inside the JavaScript Engine 5 min read
• Parsing, AST, and Bytecode 5 min read
• JIT Compilation and Hidden Classes 5 min read
• Memory and Garbage Collection 5 min read
• Memory Leaks in Practice 5 min read
• Performance Profiling and Optimization 5 min read
• Interview Lens: Engine and Performance Questions 5 min read

Module 14: Interview Synthesis

Interview Synthesis - Arun Selvam (Apple) leads, all founders contribute — 6 Topics

• What You Now Know 5 min read
• The Complete Interview Question Map 5 min read
• The Stuck Protocol: What to Do When Your Mind Goes Blank 5 min read
• The 30-Day Interview Prep Plan 5 min read
• Mock Interview: A Worked Example 5 min read
• Founder Stories: The Full Rejection Arc 5 min read

Module 15: Capstone: Building One Thing End-to-End

Capstone: Building One Thing End-to-End - Olena Marchenko, multi-voice for question bank — 6 Topics

• The Project: What We're Building 5 min read
• Setting Up: Modules, Build Tools, Structure 5 min read
• The Data Layer: Fetching, Caching, Promises 5 min read
• The UI Layer: DOM, Events, Rendering 5 min read
• Putting It Together: State, Errors, Performance 5 min read
• Interview Question Bank: Full Answers Across the Course 5 min read

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