02 · Core

Browser

Rendering, the event loop, storage, and the runtime your code lives in.

Browser question bank → 32 questions · 5 categories

How the browser turns bytes into pixels — and why your app is slow. The "explain what happens when…" questions live here.

Architecture & engines

Topic	Difficulty	Time	Tags	Best Resources
Browser high-level architecture (multi-process)	🟡	1h	`#internals`	Inside a modern browser (part 1) ⭐
Process/thread model (renderer, GPU, network)	🟡	45m	`#internals`	Inside a modern browser (part 2) ⭐
Blink rendering engine	🟡	30m	`#internals`	Chromium: Blink ⭐
V8 & JIT compilation	🔴	1.5h	`#internals` `#v8`	V8 blog ⭐
SpiderMonkey / JavaScriptCore (other engines)	🟡	30m	`#internals`	MDN: JS engines ⭐
Hidden classes & inline caches	🔴	1h	`#v8` `#performance`	V8: hidden classes ⭐

The rendering pipeline

Topic	Difficulty	Time	Tags	Best Resources
Critical rendering path (overview)	🔴	1.5h	`#rendering`	web.dev: CRP ⭐
HTML parsing & the DOM tree	🟡	45m	`#parsing` `#dom`	MDN: how browsers work ⭐
CSS parsing & the CSSOM	🟡	45m	`#parsing` `#css`	web.dev: CSSOM ⭐
Render tree, Layout & Reflow	🔴	1h	`#rendering` `#performance`	Inside a modern browser (part 3) ⭐
Paint & layers	🟡	45m	`#rendering`	web.dev: rendering perf ⭐
Compositing & the compositor thread	🔴	1h	`#rendering` `#performance`	Inside a modern browser (part 3) ⭐
Rasterization & the GPU	🔴	45m	`#rendering` `#gpu`	web.dev: animations guide ⭐
Main thread vs compositor thread	🔴	45m	`#performance`	web.dev: long tasks ⭐
Render-blocking resources	🟡	45m	`#rendering` `#performance`	web.dev ⭐

Event loop & scheduling

Topic	Difficulty	Time	Tags	Best Resources
Event loop (browser)	🟡	1h	`#async` `#internals`	Jake Archibald: in the loop ⭐
Microtasks vs macrotasks	🟡	45m	`#async`	MDN: microtasks ⭐
`requestAnimationFrame`	🟡	30m	`#rendering` `#async`	MDN: rAF ⭐
`requestIdleCallback` & scheduling	🟡	30m	`#async` `#performance`	MDN: rIC ⭐
`scheduler.postTask` / yielding	🔴	45m	`#async` `#modern`	web.dev: optimize long tasks ⭐

Memory & storage

Topic	Difficulty	Time	Tags	Best Resources
Memory management	🔴	1h	`#memory`	MDN: memory management ⭐
Garbage collection (mark & sweep)	🔴	45m	`#memory` `#v8`	V8: trash talk ⭐
Memory leaks & detection	🔴	1h	`#memory` `#performance`	Chrome DevTools: memory ⭐
Storage internals (cache/quota)	🟡	45m	`#storage`	web.dev: storage ⭐

❓ Rapid-fire browser internals interview questions

Real "how does the browser work" interview questions. Answer out loud, then verify above.

Walk through the rendering pipeline: parse → layout → paint → composite.
What is the critical rendering path and what blocks it?
Reflow vs repaint vs composite — which are expensive?
Explain the event loop, the call stack, and the task queues.
Microtasks vs macrotasks — what runs first?
What is requestAnimationFrame vs requestIdleCallback?
How does the browser build the DOM and CSSOM?
What is the compositor thread and why does it matter?
How does garbage collection (mark & sweep) work?
What causes and how do you find memory leaks?
What is V8 and how does JIT compilation work?
Why are transform/opacity animations cheaper than top/left?
What is a long task and how do you break it up?
What is the difference between the main thread and web workers?
How does the browser's multi-process architecture work?

Related: 01-fundamentals · 03-javascript · 09-performance

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