This was a lot more than just 'write some JS.' I started with a closure-based module pattern which felt right, but then got into the weeds on timer drift pretty fast.
Start by clarifying requirements and edge cases (e.g., FPS changes during playback, seeking while paused). Then outline a closure-based design that encapsulates state (current frame, FPS, timer ID, playing status) and exposes a clean API. Finally, discuss timer scheduling using setTimeout with dynamic delay based on FPS, and mention trade-offs like drift and precision.
Pro tip: Use setTimeout with a recursive scheduling function instead of setInterval to avoid drift and allow dynamic FPS changes; also, consider using requestAnimationFrame for smoother playback if the environment supports it.
Ask about expected behavior when FPS changes during playback, seeking while paused, and handling large frame jumps. Confirm the API surface and any constraints (e.g., browser vs Node).
Define a factory function that returns an object with methods. Inside, keep private variables: currentFrame, fps, isPlaying, timerId, and lastTimestamp. This ensures state is not exposed directly.
Use a recursive setTimeout function that calculates the next delay as 1000/fps. On each tick, increment currentFrame and reschedule if still playing. Clear the timer on pause or FPS change.
Implement play, pause, seek, setFPS, and getters for currentFrame and isPlaying. Ensure setFPS updates the delay for subsequent ticks without resetting the frame. Seek should clamp to valid range and optionally pause/play.
Mention potential drift with setTimeout, and how to mitigate (e.g., using performance.now() to adjust delays). Compare with setInterval and requestAnimationFrame. Suggest adding event emitters or callbacks for frame updates.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
I'd thought about this before in a different context so it wasn't totally foreign.
Start by defining the requirements of a browser media player: smooth frame updates, synchronization with audio/video, and efficient resource usage. Then compare setTimeout, setInterval, and requestAnimationFrame in terms of timing accuracy, performance, and suitability for animation. Conclude with a clear recommendation, typically requestAnimationFrame for rendering, while noting that setTimeout/setInterval may be used for non-visual tasks like polling.
Pro tip: Mention that requestAnimationFrame automatically pauses when the tab is inactive, saving battery and CPU, and that it aligns with the browser's repaint cycle, avoiding jank. This shows you understand real-world performance implications beyond just API differences.
State that a media player needs to update frames in sync with playback, often at 60fps, and must handle background tabs gracefully.
Explain that setTimeout schedules a callback after a minimum delay but is not precise; it can drift and is throttled in background tabs, leading to choppy playback.
Discuss that setInterval repeats at a fixed interval but can accumulate delays, causing overlapping calls or missed frames, and is also throttled in background tabs.
Highlight that requestAnimationFrame is optimized for animations, syncs with the browser's repaint, and pauses in background tabs, ensuring smooth and efficient rendering.
Conclude that requestAnimationFrame is the best choice for frame scheduling in a media player, while setTimeout/setInterval might be used for non-visual tasks like UI updates or polling.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by clarifying the playback system's architecture and the expected behavior for each edge case, then propose a state machine or centralized controller to manage transitions. For each edge case, describe how you would detect it, handle it gracefully, and ensure a consistent user experience.
Pro tip: Emphasize idempotency and defensive programming: operations like seeking or resuming should be safe to call multiple times without side effects. Also, mention how you would test these edge cases with unit tests and integration tests to prevent regressions.
Ask questions to understand the playback system's constraints, such as whether seeking is allowed during playback, what defines an invalid frame index, and how pause/resume should behave. State your assumptions explicitly.
Propose a state machine with states like Playing, Paused, Seeking, and Ended. Define transitions for each edge case, ensuring invalid transitions are handled gracefully (e.g., seeking while playing transitions to Seeking then back to Playing).
For each scenario, describe the detection and handling: seeking while playing (pause, seek, resume), invalid frame index (clamp to valid range or ignore with error), last frame (stop playback or loop based on requirements), and resuming after pause (restore previous state and continue).
Discuss how to make operations idempotent and thread-safe, using locks or atomic operations if needed. Mention logging and error handling for invalid inputs.
Outline a testing strategy: unit tests for each edge case, integration tests for state transitions, and possibly property-based testing to cover unexpected sequences.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.