Explain what the simple List component does?**
These simple list components in React are basically used to render different list items in React using map method. In the given code the 'WrappedListComponent' takes an array of objects called 'items' as props ,and then using the 'map' function, the component iterates through the each 'items' array and renders a 'SingleListItem' component for each object.
The 'index' prop is unique for each 'SingleListItem' component which is taken with anb key attribute and helps to identify and target the particular clicked list item.
The "isSeletedUp" props is used here as a conditional rendering as if items is selected it will ensure that the background colour is changed to green and all those list item which are not selected will remain as it is with red background.
To avoid unnecessary re-rendering of the items, the 'WrappedSingleListItem' component is memoized using memo and only re-renders when the value of the 'isSelected' prop changes. This ensures that the components will not render again even if user click it on list item again.this also adds up in the good functioning of the code without any side effects which sometimes gets added up in such cases.
2)What problems/warnings are there with the code?
problem1:
prop_typesWEBPACK_IMPORTED_MODULE2default(...).shapeOf is not a function
TypeError: prop_typesWEBPACK_IMPORTED_MODULE2default(...).shapeOf is not a function
Given code is :
WrappedListComponent.propTypes = {
items: PropTypes.array(PropTypes.shapeOf({ //ShapeOf is not a Valid Function
text: PropTypes.string.isRequired,
})),
};
Corrected and Modified code is as follows 👍
WrappedListComponent.propTypes = {
items: PropTypes.arrayOf(PropTypes.shape({ //Correct Function is ArrayOf
text: PropTypes.string.isRequired,
})),
};
problem 2:
The onClickHandler property in WrappedSingleListfunction is incorrectly used; there should be a callback function that will be called when the list item is clicked.
Error in the Console :
Uncaught TypeError: setSelectedIndex is not a function in the code given. The useState function used in the WrappedListComponent component initialises the selectedIndex state, but the initial value (null) should appear first in the returned array, not the setter function.
Given code is
const [setSelectedIndex, selectedIndex] = useState(); //invalid syntax
The corrected and Modified code is 👍
const [SelectedIndex, setSelectedIndex] = useState(); //valid syntax
Problem 4
In the map function, the value of the unique key is not defined as a prop for each child value which is very important while rendering the list this may give a warning in the console.
WARNING in the console : Warning: Each child in a list should have a unique "key" prop.
The corrected and Modified code is as follows 👍
return (
<ul style={{ textAlign: 'left' }}>
{items.map((item, index) => (
<SingleListItem
//key added to select the specific item
key={index}
onClickHandler={() => handleClick(index)}
text={item.text}
index={index}
isSelected={selectedIndex=== index}
/>
))}
)
};
problem 5:
To ensure that only the clicked option changes color and not all the content present in a list, we can modify the isSelected property to isSelected = (SelectedIndex === Index). This will allow us to update the selected option's color based on its index in the list.
given code is as follows
return (
<ul style={{ textAlign: 'left' }}>
{items.map((item, index) => (
<SingleListItem
onClickHandler={() => handleClick(index)}
text={item.text}
index={index}
isSelected={selectedIndex} // using this syntax, all available items are selected instead of any one
/>
))}
)};
The modified and corrected code is as follows 👍
return (
<ul style={{ textAlign: 'left' }};
{items.map((item, index) => (
<SingleListItem
onClickHandler={() => handleClick(index)}
text={item. text}
index={index}
//This addition of (=== index) below ensures that in the selected list items only changes is visible.
isSelected={selectedIndex=== index}
/>
))}
)};
problem 6:
The default value of null for the items prop in WrappedListComponent can lead to issues when map method is applied in it, so some dummy data has to be added in this so that while mapping with the items there's no such error.
//unadded key attribute in the code and (===index)
// return (
// <ul style={{ textAlign: 'left' }}>
// {items.map((item, index) => (
// <SingleListItem
// onClickHandler={() => handleClick(index)}
// text={item.text}
// index={index}
// isSelected={selectedIndex}
// />
// ))}
//
// )
return (
<ul style={{ textAlign: "left" }}>
{items.map((item, index) => (
<SingleListItem
key={index} //added the key attribute which was not there intially
onClickHandler={() => handleClick(index)}
text={item.text}
index={index}
isSelected={selectedIndex === index} //Modified (=== index) for targeting the specific list item
/>
))}
);
};
WrappedListComponent.propTypes = {
//invalid syntax of array and shape of
// items: PropTypes.array(PropTypes.shapeOf({
//changed array to --- arrayOf and shapeOf to -- shape
items: PropTypes.arrayOf(
PropTypes.shape({
text: PropTypes.string.isRequired,
})
),
};
WrappedListComponent.defaultProps = {
//added some dummy data instaed of null .so there is no such problem found while mapping
items: [
{ text: "Mritunjay" },
{ text: "Lovely Professional University" },
{ text: "India" },
{ text: "Europe" },
{ text: "Singapore" },
],
};
const List = memo(WrappedListComponent);
export default List;
Explain what the simple List component does?** These simple list components in React are basically used to render different list items in React using map method. In the given code the 'WrappedListComponent' takes an array of objects called 'items' as props ,and then using the 'map' function, the component iterates through the each 'items' array and renders a 'SingleListItem' component for each object. The 'index' prop is unique for each 'SingleListItem' component which is taken with anb key attribute and helps to identify and target the particular clicked list item. The "isSeletedUp" props is used here as a conditional rendering as if items is selected it will ensure that the background colour is changed to green and all those list item which are not selected will remain as it is with red background. To avoid unnecessary re-rendering of the items, the 'WrappedSingleListItem' component is memoized using memo and only re-renders when the value of the 'isSelected' prop changes. This ensures that the components will not render again even if user click it on list item again.this also adds up in the good functioning of the code without any side effects which sometimes gets added up in such cases.
2)What problems/warnings are there with the code?
problem1: prop_typesWEBPACK_IMPORTED_MODULE2default(...).shapeOf is not a function TypeError: prop_typesWEBPACK_IMPORTED_MODULE2default(...).shapeOf is not a function
Given code is :
WrappedListComponent.propTypes = { items: PropTypes.array(PropTypes.shapeOf({ //ShapeOf is not a Valid Function text: PropTypes.string.isRequired, })), };
Corrected and Modified code is as follows 👍
WrappedListComponent.propTypes = { items: PropTypes.arrayOf(PropTypes.shape({ //Correct Function is ArrayOf text: PropTypes.string.isRequired, })), };
problem 2:
The onClickHandler property in WrappedSingleListfunction is incorrectly used; there should be a callback function that will be called when the list item is clicked.
Given code is
const WrappedSingleListItem = ({ index, isSelected, onClickHandler, text, }) => { return ( <li style={{ backgroundColor: isSelected ? 'green': 'red'}}
//callback is not defined in the below onClick event:
onClick={onClickHandler(index)}> {text} ); };
The corrected and Modified code is as follows 👍
const WrappedSingleListItem = ({ index, isSelected, onClickHandler, text, }) => { return ( <li style={{ backgroundColor: isSelected ? 'green' : 'red'}} onClick={() => onClickHandler(index)}> //callback defined {text}
); };
problem 3
Error in the Console : Uncaught TypeError: setSelectedIndex is not a function in the code given. The useState function used in the WrappedListComponent component initialises the selectedIndex state, but the initial value (null) should appear first in the returned array, not the setter function.
Given code is const [setSelectedIndex, selectedIndex] = useState(); //invalid syntax
The corrected and Modified code is 👍 const [SelectedIndex, setSelectedIndex] = useState(); //valid syntax
Problem 4 In the map function, the value of the unique key is not defined as a prop for each child value which is very important while rendering the list this may give a warning in the console. WARNING in the console : Warning: Each child in a list should have a unique "key" prop.
Given code : return ( <ul style={{ textAlign: 'left' }}> {items.map((item, index) => ( <SingleListItem onClickHandler={() => handleClick(index)} text={item.text} index={index} isSelected={selectedIndex=== index} /> ))}
) };
The corrected and Modified code is as follows 👍 return ( <ul style={{ textAlign: 'left' }}> {items.map((item, index) => ( <SingleListItem //key added to select the specific item key={index} onClickHandler={() => handleClick(index)} text={item.text} index={index} isSelected={selectedIndex=== index} /> ))}
) };
problem 5: To ensure that only the clicked option changes color and not all the content present in a list, we can modify the isSelected property to isSelected = (SelectedIndex === Index). This will allow us to update the selected option's color based on its index in the list.
given code is as follows return ( <ul style={{ textAlign: 'left' }}> {items.map((item, index) => ( <SingleListItem onClickHandler={() => handleClick(index)} text={item.text} index={index} isSelected={selectedIndex} // using this syntax, all available items are selected instead of any one /> ))} )};
The modified and corrected code is as follows 👍 return ( <ul style={{ textAlign: 'left' }}; {items.map((item, index) => ( <SingleListItem onClickHandler={() => handleClick(index)} text={item. text} index={index}
))} )};
problem 6: The default value of null for the items prop in WrappedListComponent can lead to issues when map method is applied in it, so some dummy data has to be added in this so that while mapping with the items there's no such error.
The given code is as follows
WrappedListComponent.defaultProps = { items: null, };
The corrected and modified code is 👍
WrappedListComponent.defaultProps = { items: [ {text : "Mritunjay"}, {text: "Lovely Professional University"}, ], };
3)Please fix, optimize, and/or modify the component as much as you think is necessary.
import React, { useState, useEffect, memo } from "react"; import PropTypes from "prop-types";
// Single List Item const WrappedSingleListItem = ({ index, isSelected, onClickHandler, text }) => { return ( <li style={{ backgroundColor: isSelected ? "green" : "red" }} // callback is not defined intially // onClick={onClickHandler(index)}
//onclick with a callback function is defined. onClick={() => onClickHandler(index)}
WrappedSingleListItem.propTypes = { index: PropTypes.number, isSelected: PropTypes.bool, onClickHandler: PropTypes.func.isRequired, text: PropTypes.string.isRequired, };
const SingleListItem = memo(WrappedSingleListItem);
// List Component const WrappedListComponent = ({ items }) => { // const [setSelectedIndex, selectedIndex] = useState(); // intial code given with invalid syntax
const [selectedIndex, setSelectedIndex] = useState(); //Modified code with correct syntax
useEffect(() => { setSelectedIndex(null); }, [items]);
const handleClick = (index) => { setSelectedIndex(index); };
//unadded key attribute in the code and (===index)
// return ( // <ul style={{ textAlign: 'left' }}> // {items.map((item, index) => ( // <SingleListItem // onClickHandler={() => handleClick(index)} // text={item.text} // index={index} // isSelected={selectedIndex} // /> // ))} // // ) return ( <ul style={{ textAlign: "left" }}> {items.map((item, index) => ( <SingleListItem key={index} //added the key attribute which was not there intially onClickHandler={() => handleClick(index)} text={item.text} index={index} isSelected={selectedIndex === index} //Modified (=== index) for targeting the specific list item /> ))}
); };
WrappedListComponent.propTypes = { //invalid syntax of array and shape of // items: PropTypes.array(PropTypes.shapeOf({
//changed array to --- arrayOf and shapeOf to -- shape items: PropTypes.arrayOf( PropTypes.shape({ text: PropTypes.string.isRequired, }) ), };
WrappedListComponent.defaultProps = { //added some dummy data instaed of null .so there is no such problem found while mapping items: [ { text: "Mritunjay" }, { text: "Lovely Professional University" }, { text: "India" }, { text: "Europe" }, { text: "Singapore" }, ], }; const List = memo(WrappedListComponent); export default List;