Enhancing performance with React.memo and TypeScript

Question

Enhancing performance with React.memo and TypeScript

I am currently developing a react native application. I am using the Item component within a flatlist to display data, however, I encountered an error in the editor regarding the second parameter of React.memo:

The error message reads: 'Type 'boolean | undefined' is not assignable to type 'boolean'. Type 'undefined' is not assignable to type 'boolean'.

const Item = React.memo(
    ({ icon, title }: any) => {
        return (
            <Box
                flexDirection="row"
                paddingHorizontal="l"
                justifyContent="space-between"
                alignItems="center"
                style={{ marginTop: 35 }}
            >
                <Box flexDirection="row" alignItems="center" flex={1}>
                    {icon}

                    <Box marginLeft="l">
                        <Text  variant="stackHeader">{title}</Text>
                        <Text
                            fontSize={15}
                            fontFamily="CrimsonRegular"
                            style={{ color: '#575757' }}
                        >
                            Last update: 03/06/2020
                        </Text>
                    </Box>
                </Box>
                <TouchableOpacity onPress={() => Clipboard.setString(title as string)}>
                <FontAwesome5 name="copy" size={28} color="white" />
                </TouchableOpacity>
            </Box>
        );
    },
    (prev, next) => { // This is where the error occurs
        if (prev.title === next.title) {
            return true;
        }
    }
);

typescript react-native react-memo

Answer 1

Answer №1

(first, second) => { // error here
    if (first.name === second.name) {
        return true;
    }
}

When working with Typescript, it is important for your function to consistently return a boolean value. In this case, the function only returns true under certain conditions, resulting in a potential return of undefined, which does not equate to the boolean value false.

To resolve this issue, ensure that your function always has a return statement for all conditional paths.

An alternative approach would be to include an else clause in your conditional statement that explicitly returns false.

(first, second) => {
    if (first.name === second.name) {
        return true;
    } else {
        return false;
    }
}

This can be simplified to:

(first, second) => {
    return first.name === second.name;
}

Answer 2

(first, second) => { // error here
    if (first.name === second.name) {
        return true;
    }
}

When working with Typescript, it is important for your function to consistently return a boolean value. In this case, the function only returns true under certain conditions, resulting in a potential return of undefined, which does not equate to the boolean value false.

To resolve this issue, ensure that your function always has a return statement for all conditional paths.

An alternative approach would be to include an else clause in your conditional statement that explicitly returns false.

(first, second) => {
    if (first.name === second.name) {
        return true;
    } else {
        return false;
    }
}

This can be simplified to:

(first, second) => {
    return first.name === second.name;
}

Answer 3

Answer №2

In reality, the function anticipates a boolean value as the return type, which is why this code snippet could be beneficial:

(previous, next) => {
   return previous.title === next.title;
 }

Answer 4

In reality, the function anticipates a boolean value as the return type, which is why this code snippet could be beneficial:

(previous, next) => {
   return previous.title === next.title;
 }

Enhancing performance with React.memo and TypeScript

Answer №1

Answer №2

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