Split Pane: Implement a UI Split Pane Component With Draggable Divider and Min/Max Constraints
Question Details
Problem
Build a split pane UI component in JavaScript/TypeScript. The component divides a container into two resizable panels separated by a draggable divider. Each panel has a minSize (px) and optionally a maxSize. The divider cannot be dragged past these constraints.
typescript
class SplitPane {
constructor(
container: HTMLElement,
direction: 'horizontal' | 'vertical',
options: {
initialSplit: number, // 0-1, fraction for first pane
minSizes: [number, number],
maxSizes?: [number | null, number | null]
}
) {}
setSplit(fraction: number): void {}
getSplit(): number {}
onResize(callback: (fraction: number) => void): void {}
}
Example behavior:
const pane = new SplitPane(container, 'horizontal', {
initialSplit: 0.5, minSizes: [100, 100]
});
// User drags divider left; pane A shrinks to minSize=100px and stops
Follow-ups
- Which mouse/touch events do you attach and where — on the divider, document, or container?
- How do you handle resize of the outer container (e.g., browser window resize) without violating constraints?
- How would you persist the split position in localStorage and restore it on load?
- Extend to a three-panel layout — what data structure represents nested splits?
Full Details
Problem
Build a split pane UI component in JavaScript/TypeScript. The component divides a container into two resizable panels separated by a draggable divider. Each panel has a minSize (px) and optionally a maxSize. The divider cannot be dragged past these constraints.
typescript
class SplitPane {
constructor(
container: HTMLElement,
direction: 'horizontal' | 'vertical',
options: {
initialSplit: number, // 0-1, fraction for first pane
minSizes: [number, number],
maxSizes?: [number | null, number | null]
}
) {}
setSplit(fraction: number): void {}
getSplit(): number {}
onResize(callback: (fraction: number) => void): void {}
}
Example behavior:
const pane = new SplitPane(container, 'horizontal', {
initialSplit: 0.5, minSizes: [100, 100]
});
// User drags divider left; pane A shrinks to minSize=100px and stops
Follow-ups
- Which mouse/touch events do you attach and where — on the divider, document, or container?
- How do you handle resize of the outer container (e.g., browser window resize) without violating constraints?
- How would you persist the split position in localStorage and restore it on load?
- Extend to a three-panel layout — what data structure represents nested splits?
About This Question
This is a reported interview question from a warp interview during the phone round.
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This question was reported by a candidate who interviewed at Warp. LeakCode aggregates interview reports from 10+ sources, including 1Point3Acres, Glassdoor, LeetCode Discuss, Blind, Reddit, Indeed, and Nowcoder. Each report is translated where necessary, deduplicated against existing entries, and tagged by company, role, round type, and reporting date.
Use this question as one calibration data point, not a memorization target. Companies typically rotate their question pools every 2-4 months; the exact wording of a 2024 question may differ from what you encounter today. The underlying pattern, difficulty level, and follow-up depth at Warp are the higher-signal extractions to take from this report.
For broader preparation context, the Warp interview process typically includes a recruiter screen, one or two technical phone screens, and a 4-5 round on-site loop covering coding, system design (at L4+ levels), and behavioral. Reports tagged on LeakCode show the round-by-round distribution and typical difficulty calibration. To browse questions filtered by round type and seniority, use the company hub linked above.
How To Practice This Type of Question
Solve similar problems on LeetCode under timed conditions (25-35 minutes per medium difficulty). The goal is pattern recognition: recognize the underlying technique (sliding window, two-pointer, BFS, memoized recursion, etc.) within 60-90 seconds of reading. Strong candidates verbalize their hypothesis out loud before coding, then iterate based on feedback. Weak candidates dive into implementation immediately, lose time on the wrong approach, and run out of time for follow-ups.
Companies update their question pools every 2-4 months. The exact wording of any given question may have been retired by the time you interview. Focus your prep on the pattern, not the specific problem. The patterns that appear in Warp reports consistently are the ones worth investing in; one-off niche problems are not.
During Your Warp Round
Apply the standard interview round template: clarify requirements (2-3 minutes), state your approach out loud and confirm direction with the interviewer (3-5 minutes), code with narration (15-25 minutes), test with concrete examples including edge cases (5 minutes), discuss optimization or trade-offs if time permits (5 minutes). This template is universally accepted across FAANG and adjacent companies; deviating from it produces weaker interviewer feedback signal.
The single most predictive failure mode in Warp reports tagged "no hire": not asking clarifying questions. Interviewers are explicitly trained to weight this. Strong candidates ask 3-5 clarifying questions even on problems that look obvious; weak candidates dive into code immediately. The clarifying-question check is often the first signal recorded in the interviewer's written notes.