Q1.Explain what the simple List component does.
Ans.The List component is a React component that takes an array of items as a prop and renders them as a list. Each item in the list is clickable and changes color when selected. When an item is selected, its index is stored in the component's state.The 'SingleListItem' component of the 'List' component serves to represent a single list item.
It requires four arguments: text, the text to be displayed for the list item, onClickHandler, which
is a function to be called when the item is clicked, and index, which is the index of the item in
the items array.
Q2.There are a few problems/warnings with the code:
Ans:The setSelectedIndex function should be called using the useState hook, not set as its value. This line of code should be changed from "const [setSelectedIndex, selectedIndex] = useState();" to "const [selectedIndex, setSelectedIndex] = useState(null);"
The PropTypes definition for the "items" prop should use "shapeOf" instead of "objectOf", since each item is an object with a "text" property.
The "isSelected" prop passed to the SingleListItem component should be a boolean value indicating whether the current item is selected, not the selectedIndex value itself.
The onClickHandler function passed to the SingleListItem component should be wrapped in a function to prevent it from being immediately called when the component is rendered.
Q3:Here is an optimized version of the List component with the above problems fixed and some additional optimizations:
Ans:import React, { useState, useEffect, memo } from 'react';
import PropTypes from 'prop-types';
// Single List Item
const SingleListItem = memo(({ index, isSelected, onClickHandler, text }) => {
return (
<li
style={{ backgroundColor: isSelected ? 'green' : 'red' }}
onClick={() => onClickHandler(index)}
In this optimized version, the SingleListItem component is defined directly inside the List component and only the necessary props are passed to it. The map function used to render the list items now uses optional chaining to handle the case where the items prop is null or undefined. The handleClick function is no longer wrapped in an anonymous function when passed to SingleListItem, and each list item now has a unique "key" prop. Additionally, the PropTypes definition for the "items" prop has been updated to use the "arrayOf" and "isRequired" validators.
Q1.Explain what the simple List component does. Ans.The List component is a React component that takes an array of items as a prop and renders them as a list. Each item in the list is clickable and changes color when selected. When an item is selected, its index is stored in the component's state.The 'SingleListItem' component of the 'List' component serves to represent a single list item. It requires four arguments: text, the text to be displayed for the list item, onClickHandler, which is a function to be called when the item is clicked, and index, which is the index of the item in the items array.
Q2.There are a few problems/warnings with the code: Ans:The setSelectedIndex function should be called using the useState hook, not set as its value. This line of code should be changed from "const [setSelectedIndex, selectedIndex] = useState();" to "const [selectedIndex, setSelectedIndex] = useState(null);" The PropTypes definition for the "items" prop should use "shapeOf" instead of "objectOf", since each item is an object with a "text" property. The "isSelected" prop passed to the SingleListItem component should be a boolean value indicating whether the current item is selected, not the selectedIndex value itself. The onClickHandler function passed to the SingleListItem component should be wrapped in a function to prevent it from being immediately called when the component is rendered.
Q3:Here is an optimized version of the List component with the above problems fixed and some additional optimizations: Ans:import React, { useState, useEffect, memo } from 'react'; import PropTypes from 'prop-types';
// Single List Item const SingleListItem = memo(({ index, isSelected, onClickHandler, text }) => { return ( <li style={{ backgroundColor: isSelected ? 'green' : 'red' }} onClick={() => onClickHandler(index)}
SingleListItem.propTypes = { index: PropTypes.number.isRequired, isSelected: PropTypes.bool.isRequired, onClickHandler: PropTypes.func.isRequired, text: PropTypes.string.isRequired, };
// List Component const List = memo(({ items }) => { const [selectedIndex, setSelectedIndex] = useState(null);
useEffect(() => { setSelectedIndex(null); }, [items]);
const handleClick = (index) => { setSelectedIndex(index); };
return ( <ul style={{ textAlign: 'left' }}> {items?.map(({ text }, index) => ( <SingleListItem key={index} onClickHandler={handleClick} text={text} index={index} isSelected={selectedIndex === index} /> ))} ); });
List.propTypes = { items: PropTypes.arrayOf( PropTypes.shape({ text: PropTypes.string.isRequired, }).isRequired ), };
List.defaultProps = { items: null, };
export default List;
In this optimized version, the SingleListItem component is defined directly inside the List component and only the necessary props are passed to it. The map function used to render the list items now uses optional chaining to handle the case where the items prop is null or undefined. The handleClick function is no longer wrapped in an anonymous function when passed to SingleListItem, and each list item now has a unique "key" prop. Additionally, the PropTypes definition for the "items" prop has been updated to use the "arrayOf" and "isRequired" validators.