JavaScript Deep Dive Roadmap

Learn the building blocks — let/const/var (and why var is problematic), primitive types (string, number, boolean, null, undefined, symbol, bigint), type coercion (== vs ===, truthy/falsy), and how typeof and instanceof work. Understand why null == undefined but null !== undefined.

Language JavaScript 6h

Master if/else, switch, for, while, do-while, for...of (iterables), for...in (object keys — and why to be careful), break/continue/return, the ternary operator, logical operators (&&, ||, ??), and short-circuit evaluation. Understand labeled statements and why nested loop breaks need labels.

Language JavaScript 5h

Understand function declarations vs expressions vs arrow functions, parameter defaults, rest parameters, lexical scope, the scope chain, hoisting (variable and function), and closures — how inner functions retain access to outer variables even after the outer function returns. Closures power private state, memoization, and factory functions.

Language JavaScript 8h

Learn object literals, computed property names, shorthand methods, getters/setters, property descriptors (writable, enumerable, configurable), the prototype chain (how [[Prototype]] links objects), Object.create(), this binding rules (implicit, explicit with call/apply/bind, new, arrow), and ES6 classes as syntactic sugar over prototypes.

Language JavaScript 8h

Use the modern JavaScript features shipped since ES2015 — destructuring (arrays, objects, nested, default values), spread/rest operators, template literals, optional chaining (?.), nullish coalescing (??), logical assignment (&&=, ||=, ??=), Array methods (map, filter, reduce, find, flat, flatMap), Object.entries/keys/values/fromEntries, and dynamic imports.

Language JavaScript 6h

Use arrays for ordered sequences and understand the full method suite (push/pop/shift/unshift, slice/splice, sort, indexOf/findIndex/includes). Use Map for key-value stores with non-string keys. Use Set for unique collections and deduplication. Know the iterable protocol (Symbol.iterator) and how for...of works with custom iterables.

Language JavaScript 6h

Master async JavaScript — the Promise constructor, then/catch/finally chaining, Promise.all (fail fast), Promise.allSettled (all results), Promise.race (first to settle), Promise.any (first success), and async/await as syntactic sugar. Understand error propagation, why unhandled promise rejections crash Node.js, and patterns for concurrent async workflows.

Language JavaScript 8h

Understand the JavaScript runtime — the call stack (synchronous execution), heap (object allocation), task queue (setTimeout, I/O callbacks), microtask queue (Promise callbacks, queueMicrotask — executes before next task), and the event loop that orchestrates them. Understand why long synchronous work blocks I/O and why Promise.resolve().then() fires before setTimeout(() =>{}, 0).

Language JavaScript 6h

Use generator functions (function*) to produce sequences lazily, understand yield, return, and throw in a generator, the iterator protocol (next(), done, value), and async generators (async function*) for async iteration with for await...of. Generators power infinite sequences, cancelable async operations, and stream processing.

Language JavaScript 5h

Handle errors correctly — try/catch/finally, rethrowing errors, custom Error subclasses (class ValidationError extends Error), error classification (operational vs programmer errors), async error propagation in Promises and async/await, the unhandledRejection event in Node.js, and the Fail Fast principle. Avoid swallowing errors silently.

Language JavaScript 5h

Apply functional programming ideas to JavaScript — pure functions and referential transparency, immutability (Object.freeze, spread for updates), higher-order functions, function composition (pipe/compose), partial application and currying, and why avoiding side effects in business logic makes code testable. Understand when to reach for libraries like Ramda.

Language JavaScript 6h

Apply classic design patterns idiomatically in JavaScript — Module pattern (IIFE, revealing module), Observer/EventEmitter, Strategy, Factory, Builder, Singleton (and why to avoid it), Decorator (stage 3 proposal), and Proxy for validation and reactive data. Know which patterns solve which problems and when they over-engineer.

Language JavaScript 7h

Use Proxy to intercept object operations (get, set, has, deleteProperty, apply) for validation, logging, reactive data binding, and access control. Use Reflect as a safe complement for forwarding operations. Understand WeakRef, FinalizationRegistry for memory-sensitive caches, and Symbol for well-known protocols (Symbol.iterator, Symbol.toPrimitive).

Language JavaScript 6h

Profile and optimize JavaScript — use Chrome DevTools Performance panel to identify long tasks, use Memory Profiler to find memory leaks (detached DOM nodes, closures holding references, forgotten event listeners), understand V8 JIT compilation hints (avoid hidden class changes), Big O analysis for algorithm choice, and benchmark with performance.now().

Language JavaScript 8h

Write JavaScript that doesn't introduce security vulnerabilities — prevent XSS by using textContent instead of innerHTML for untrusted data, understand prototype pollution attacks (and how to prevent them with null-prototype objects), safe JSON parsing, avoiding eval(), securing postMessage origins, and auditing npm dependencies for known vulnerabilities.

Language JavaScript 5h