Q.1. Explain what the simple List component does?
Answer - The List component is a React functional component that renders a list of items. It receives an array of items as a prop, where each item is an object with a text property.
The List component first defines a child component SimpleListItem that renders a single item in the list. This component receives the following props:
index: The index of the item in the items array.
isSelected: A boolean indicating whether the item is currently selected.
onClickHandler: A function to be called when the item is clicked.
text: The text to be displayed for the item.
The SimpleListItem component renders an
element with the following properties:
The background color of the item is green if isSelected is true, and red otherwise.
When the item is clicked, it calls the onClickHandler function with the index prop.
The List component then defines another child component WrappedListComponent that renders the list of items. This component receives the following props:
items: An array of objects with a text property.
The WrappedListComponent component uses the useState hook to keep track of the index of the currently selected item, and the useEffect hook to reset the selected index to null whenever the items prop changes. It also defines a handleClick function that updates the selected index when an item is clicked.
Finally, the WrappedListComponent component maps over the items array and renders a SimpleListItem component for each item. It passes the following props to each SimpleListItem component:
onClickHandler: A function that calls the handleClick function with the index of the clicked item.
text: The text property of the item.
index: The index of the item in the items array.
isSelected: A boolean indicating whether the item is currently selected.
The List component then renders a
element with the list of SimpleListItem components.
Q.2. What problems / warnings are there with code?
Answer -
There are a few errors and warnings in the given code:
In the SingleListItem component, the onClickHandler prop should be passed as a function reference, rather than invoking it immediately. The line should be changed from:
onClick={onClickHandler(index)} to
onClick={() => onClickHandler(index)}
In the WrappedListComponent component, the selectedIndex state hook is not initialized with a value, which can lead to unexpected behavior. The line should be changed from:
const [setSelectedIndex, selectedIndex] = useState(); to
const [selectedIndex, setSelectedIndex] = useState(null);
In the WrappedListComponent component, the items prop should be defined as an array of objects with a text property, rather than an array with a shape of an object. The line should be changed from:
items: PropTypes.array(PropTypes.shapeOf({
text: PropTypes.string.isRequired,
})), to
items: PropTypes.arrayOf(PropTypes.shape({
text: PropTypes.string.isRequired,
})),
In the SingleListItem component, the isSelected prop is being passed as the value of selectedIndex, which is a boolean. It should be passed as a comparison between index and selectedIndex, like this:
isSelected={index === selectedIndex}
Q.3. Please fix, optimize, and/or modify the component as much as you think is necessary.
Answer- Here's a modified version of the List component that addresses the issues in the original code and makes some optimizations and improvements:
import React, { useState, useCallback } from 'react';
import PropTypes from 'prop-types';
// Single List Item
const SingleListItem = React.memo(({ index, isSelected, onClick, text }) => {
return (
<li
style={{ backgroundColor: isSelected ? 'green' : 'red' }}
onClick={() => onClick(index)}
The SimpleListItem component is now declared using the React.memo function to optimize rendering. This ensures that the component is only re-rendered when its props have changed.
The SimpleListItem component now uses a function reference for the onClick prop, which is defined using the useCallback hook to prevent unnecessary re-renders of the List component.
The List component now specifies the isRequired property for the items prop and removes the default value.
The List component now uses the key prop when rendering the SimpleListItem components to improve performance and avoid warning messages.
The List component now passes the handleClick function as a prop to each SimpleListItem component, which simplifies the code and makes it easier to understand.
The List component now uses strict equality (===) to compare the index of the current item with the selected index to determine whether the item is selected.
Overall, these changes improve the performance and readability of the List component.
Q.1. Explain what the simple List component does? Answer - The List component is a React functional component that renders a list of items. It receives an array of items as a prop, where each item is an object with a text property.
The List component first defines a child component SimpleListItem that renders a single item in the list. This component receives the following props:
index: The index of the item in the items array. isSelected: A boolean indicating whether the item is currently selected. onClickHandler: A function to be called when the item is clicked. text: The text to be displayed for the item. The SimpleListItem component renders an
element with the following properties: The background color of the item is green if isSelected is true, and red otherwise. When the item is clicked, it calls the onClickHandler function with the index prop. The List component then defines another child component WrappedListComponent that renders the list of items. This component receives the following props: items: An array of objects with a text property. The WrappedListComponent component uses the useState hook to keep track of the index of the currently selected item, and the useEffect hook to reset the selected index to null whenever the items prop changes. It also defines a handleClick function that updates the selected index when an item is clicked.
Finally, the WrappedListComponent component maps over the items array and renders a SimpleListItem component for each item. It passes the following props to each SimpleListItem component:
onClickHandler: A function that calls the handleClick function with the index of the clicked item. text: The text property of the item. index: The index of the item in the items array. isSelected: A boolean indicating whether the item is currently selected. The List component then renders a
element with the list of SimpleListItem components. Q.2. What problems / warnings are there with code? Answer - There are a few errors and warnings in the given code:
In the SingleListItem component, the onClickHandler prop should be passed as a function reference, rather than invoking it immediately. The line should be changed from: onClick={onClickHandler(index)} to onClick={() => onClickHandler(index)}
In the WrappedListComponent component, the selectedIndex state hook is not initialized with a value, which can lead to unexpected behavior. The line should be changed from: const [setSelectedIndex, selectedIndex] = useState(); to const [selectedIndex, setSelectedIndex] = useState(null);
In the WrappedListComponent component, the items prop should be defined as an array of objects with a text property, rather than an array with a shape of an object. The line should be changed from: items: PropTypes.array(PropTypes.shapeOf({ text: PropTypes.string.isRequired, })), to items: PropTypes.arrayOf(PropTypes.shape({ text: PropTypes.string.isRequired, })),
In the SingleListItem component, the isSelected prop is being passed as the value of selectedIndex, which is a boolean. It should be passed as a comparison between index and selectedIndex, like this: isSelected={index === selectedIndex}
Q.3. Please fix, optimize, and/or modify the component as much as you think is necessary. Answer- Here's a modified version of the List component that addresses the issues in the original code and makes some optimizations and improvements:
import React, { useState, useCallback } from 'react'; import PropTypes from 'prop-types';
// Single List Item const SingleListItem = React.memo(({ index, isSelected, onClick, text }) => { return ( <li style={{ backgroundColor: isSelected ? 'green' : 'red' }} onClick={() => onClick(index)}
); });
SingleListItem.propTypes = { index: PropTypes.number.isRequired, isSelected: PropTypes.bool.isRequired, onClick: PropTypes.func.isRequired, text: PropTypes.string.isRequired, };
// List Component const List = ({ items }) => { const [selectedIndex, setSelectedIndex] = useState(null);
const handleClick = useCallback((index) => { setSelectedIndex(index); }, []);
return ( <ul style={{ textAlign: 'left' }}> {items.map((item, index) => ( <SingleListItem key={index} onClick={handleClick} text={item.text} index={index} isSelected={index === selectedIndex} /> ))}
); }; List.propTypes = { items: PropTypes.arrayOf( PropTypes.shape({ text: PropTypes.string.isRequired, }) ).isRequired, };
export default List;
Here's what's changed:
The SimpleListItem component is now declared using the React.memo function to optimize rendering. This ensures that the component is only re-rendered when its props have changed.
The SimpleListItem component now uses a function reference for the onClick prop, which is defined using the useCallback hook to prevent unnecessary re-renders of the List component.
The List component now specifies the isRequired property for the items prop and removes the default value.
The List component now uses the key prop when rendering the SimpleListItem components to improve performance and avoid warning messages.
The List component now passes the handleClick function as a prop to each SimpleListItem component, which simplifies the code and makes it easier to understand.
The List component now uses strict equality (===) to compare the index of the current item with the selected index to determine whether the item is selected.
Overall, these changes improve the performance and readability of the List component.