ReactJS Program to Preload Lazy Panel On Hover with Explanation
ReactJS
Hard
Performance & Patterns
19 views
1 min read
91 words
This problem helps you practice core ReactJS fundamentals in a practical way. It builds intuition around preload, lazy, hover. Let’s break it down step by step so you can implement it confidently.
Problem Statement
Preload a lazy component when user hovers so it opens instantly.
Input Format
No input.
Output Format
Render a React component.
Constraints
Keep a separate preload() that calls the same dynamic import.
Code Solution
This explanation is written for learning purposes and to help beginners understand the concept clearly.
import React, { Suspense, useState } from 'react';
const loadPanel = () => import('./MeetcodePanel');
const LazyPanel = React.lazy(loadPanel);
export default function App() {
const [open, setOpen] = useState(false);
return (
<div style={{ padding: 16, width: 520 }}>
<h2 style={{ marginTop: 0 }}>Lazy panel</h2>
<button
type='button'
onMouseEnter={() => { loadPanel(); }}
onFocus={() => { loadPanel(); }}
onClick={() => setOpen((v) => !v)}
style={{ padding: '10px 14px', borderRadius: 12, border: 0, background: '#0b5', color: '#fff' }}
>
{open ? 'Close' : 'Open'} panel
</button>
{open ? (
<div style={{ marginTop: 12, border: '1px solid #eee', borderRadius: 14, padding: 12 }}>
<Suspense fallback={<div style={{ color: '#555' }}>Loading meetcode panel...</div>}>
<LazyPanel />
</Suspense>
</div>
) : null}
</div>
);
}
Output Example
No sample I/O is provided for this question.
Common Mistakes
- Misreading input/output format.
- Not handling constraints and edge cases.
- Off-by-one errors in loops.
- Forgetting to reset variables between test cases (if any).
Solution Guide
Problem
Preload a lazy component when user hovers so it opens instantly.
Input / Output
Output
Render a React component.
Constraints
Keep a separate preload() that calls the same dynamic import.
Details
Common Mistakes
- Misreading input/output format.
- Not handling constraints and edge cases.
- Off-by-one errors in loops.
- Forgetting to reset variables between test cases (if any).
Official Solution
import React, { Suspense, useState } from 'react';
const loadPanel = () => import('./MeetcodePanel');
const LazyPanel = React.lazy(loadPanel);
export default function App() {
const [open, setOpen] = useState(false);
return (
<div style={{ padding: 16, width: 520 }}>
<h2 style={{ marginTop: 0 }}>Lazy panel</h2>
<button
type='button'
onMouseEnter={() => { loadPanel(); }}
onFocus={() => { loadPanel(); }}
onClick={() => setOpen((v) => !v)}
style={{ padding: '10px 14px', borderRadius: 12, border: 0, background: '#0b5', color: '#fff' }}
>
{open ? 'Close' : 'Open'} panel
</button>
{open ? (
<div style={{ marginTop: 12, border: '1px solid #eee', borderRadius: 14, padding: 12 }}>
<Suspense fallback={<div style={{ color: '#555' }}>Loading meetcode panel...</div>}>
<LazyPanel />
</Suspense>
</div>
) : null}
</div>
);
}
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