JavaScript Deep Dive
The language mechanics a senior is expected to explain, not just use.
17 topics
Execution Contexts, Scope & Closures
How JavaScript decides which variable a name refers to, and why a function keeps its birthplace alive long after that function has returned.
core25 minthisand Function BindingThe four rules that decide what `this` refers to, and why arrow functions ignore all of them.
core20 minPrototypes, Inheritance & Classes
Why JavaScript objects delegate to other objects rather than copy from blueprints, and what `class` is actually doing underneath.
core25 minEvent Loop, Microtasks & Macrotasks
How JavaScript schedules async work, and why a promise callback always beats a zero-delay timer.
core25 minPromises,
async/await& CombinatorsHow promise state and chaining actually work, which combinator to reach for, and where errors silently disappear.
core25 minGenerators & Async Iteration
Functions that can pause and resume, and the protocol behind `for await` and streaming responses.
deep20 minScheduling, Timers & Yielding
What `setTimeout(fn, 0)` actually promises, and how to hand the main thread back so the page stays responsive.
core20 minError Handling in JavaScript
How errors propagate through sync, async, and callback code, and why most production error reports are useless.
core20 minModules — ESM, CommonJS & Resolution
Why ESM imports are live bindings resolved before execution, and what actually breaks when a package ships both formats.
core25 minCoercion, Equality & Number Precision
The conversion rules behind JavaScript's most-mocked behaviour, and the floating-point limits that cause real money bugs.
core20 minProperty Descriptors & Immutability
What a property actually is beneath the syntax, and why `Object.freeze` protects less than people assume.
deep20 minIterables, Maps, Sets & Cloning
The protocol that makes `for...of` and spread work, and when a Map genuinely beats an object.
core20 minProxies & Reflection
Intercepting the fundamental operations on an object — the mechanism behind Immer, Vue reactivity, and most mocking libraries.
deep20 minMemory & Garbage Collection
How the engine decides what to free, and the four leak patterns that make long-lived SPA sessions degrade.
core25 minEngine Internals & Optimisation
How V8 turns your code into machine code, and the small number of habits that keep it on the fast path.
deep25 minUtilities From Scratch
The handful of implementations that show up in every live-coding screen, and what each one is really testing.
core30 minConcurrency Models
The four ways systems run more than one thing at once, and why JavaScript picked the one it did.
core25 minshared