bhavna_frontend

[bhavna90909]

In React.js, a simple list component is a component that is designed to display a list of items. It is one of the most commonly used components in React applications.

The basic structure of a simple list component in React.js involves using the map() method to iterate over an array of data and create a list of items from that data. Here is an example of a simple list component that displays a list of names:

import React from 'react';

function SimpleList({ names }) {
  return (
    <ul>
      {names.map((name, index) => (
        <li key={index}>{name}</li>
      ))}
    </ul>
  );
}

export default SimpleList;

In this example, the SimpleList component receives an array of names as a prop. It then uses the map() method to iterate over the names array and create a list item (<li>) for each name. The key prop is used to uniquely identify each list item.

This simple list component can be used in other components or in the main application to display a list of names. For example:

import React from 'react';
import SimpleList from './SimpleList';

function App() {
  const names = ['Alice', 'Bob', 'Charlie'];

  return (
    <div>
      <h1>Names:</h1>
      <SimpleList names={names} />
    </div>
  );
}

export default App;

In this example, the App component renders the SimpleList component and passes in an array of names as a prop. The SimpleList component then displays the list of names as a bulleted list.

question 2 & 3

There are several issues and warnings with the provided code:

1. The setSelectedIndex state variable is not properly initialized. It should be initialized with a default value (e.g., useState(null)), and not just declared.

2. The onClickHandler prop of the SingleListItem component is not being called correctly. It should be passed as a callback function (e.g., onClick={() => onClickHandler(index)}), and not invoked immediately (e.g., onClick={onClickHandler(index)}).

3. The isSelected prop of the SingleListItem component is not being passed correctly. It should be passed as a boolean value (e.g., isSelected={selectedIndex === index}), and not the selectedIndex state variable directly.

4. The PropTypes.array validation in the WrappedListComponent component is incorrect. It should be PropTypes.arrayOf(PropTypes.shape({...})), not PropTypes.array(PropTypes.shape({...})).

Here's an updated version of the code with the above issues fixed and some additional optimizations:

import React, { useState, useEffect, useCallback, memo } from 'react';
import PropTypes from 'prop-types';

// Single List Item
const SingleListItem = memo(({ index, isSelected, onClickHandler, text }) => {
  const handleClick = useCallback(() => {
    onClickHandler(index);
  }, [index, onClickHandler]);

  return (
    <li
      style={{ backgroundColor: isSelected ? 'green' : 'red' }}
      onClick={handleClick}
    >
      {text}
    </li>
  );
});

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 = useCallback((index) => {
    setSelectedIndex(index);
  }, []);

  return (
    <ul style={{ textAlign: 'left' }}>
      {items.map((item, index) => (
        <SingleListItem
          key={index}
          onClickHandler={handleClick}
          text={item.text}
          index={index}
          isSelected={selectedIndex === index}
        />
      ))}
    </ul>
  );
});

List.propTypes = {
  items: PropTypes.arrayOf(
    PropTypes.shape({
      text: PropTypes.string.isRequired,
    })
  ),
};

List.defaultProps = {
  items: null,
};

export default List;

In this updated version of the code:

1. The SingleListItem component now uses the useCallback hook to memoize the handleClick function and avoid unnecessary re-renders.

2. The SingleListItem component now passes the onClickHandler prop as a callback function, using the memoized handleClick function.

3. The SingleListItem component now correctly passes the isSelected prop as a boolean value, using the selectedIndex state variable.

4. The List component now correctly uses PropTypes.arrayOf to validate the items prop, and specifies the shape of each item using PropTypes.shape.

5. The List component now uses the useCallback hook to memoize the handleClick function and avoid unnecessary re-renders.

6. The List component now passes the key prop to each SingleListItem component, using the index variable.

7. The List component now uses destructuring to extract the items prop directly, instead of accessing it through the props object.