JavaScript“声明了变量但从未使用过”...即使我正在使用它？

Question

我一定是错过了什么。

在下面的代码中，我清楚地声明了

loopingAdjustment

，然后在其正下方的

fromCharCode

函数中调用它。所以，我正在使用它，对吗？我应该能够调用它，因为它在同一范围内，对吗？

为什么 Visual Studio Code 说它“从未使用过”，为什么我的终端说它“未定义”？

const caesar = function(startingString, shiftAmount) {

    let itemizedString = startingString.split('');

    const mappedLetters = itemizedString.map(stringLetter => {

        //turn each letter in array into their respective character code
        let thisLetter = stringLetter.charCodeAt(stringLetter);

        // checking if character is alphabetic and converting its charcode back to a letter
        if (thisLetter < 65 || (thisLetter > 90 && thisLetter < 97) || thisLetter > 122) {
            return;
        } else {
            shiftedLetter = thisLetter + shiftAmount;
        }

        // making sure the shifted letters loop to beginning, or end, of alphabet
        if (thisLetter > 96 && shiftedLetter > 122) {
            let loopingAdjustment = shiftedLetter - 26;
        } else if (thisLetter > 96 && shiftedLetter < 96) {
            let loopingAdjustment = shiftedLetter + 26;
        } else if (thisLetter < 91 && shiftedLetter > 90) {
            let loopingAdjustment = shiftedLetter - 26;
        } else if (thisLetter < 91 && shiftedLetter < 65) {
            let loopingAdjustment = shiftedLetter + 26;
        } else {
            let loopingAdjustment = shiftedLetter;
        }

        let finalString = String.fromCharCode(loopingAdjustment);

        return finalString;


    });

    console.log(mappedLetters);

    return mappedLetters.join('');

}

module.exports = caesar

Answer 1

发生这种情况是因为作用域，因为您仅在 if 语句内声明和定义了loopingAdjustment 变量，因此作用域仅限于 if 语句。要解决此问题，您可以在 if 外部声明循环调整并在 if 语句内部分配它。您可以参考下面的代码，您可以修改 acc.满足您的需求。

const caesar = function(startingString, shiftAmount) {
    
    let itemizedString = startingString.split('');

    const mappedLetters = itemizedString.map(stringLetter => {
        
        //turn each letter in array into their respective character code
        let thisLetter = stringLetter.charCodeAt(stringLetter);

        // checking if character is alphabetic and converting its charcode back to a letter
        if (thisLetter < 65 || (thisLetter > 90 && thisLetter < 97) || thisLetter > 122) {
            return;
        } else {
            shiftedLetter = thisLetter + shiftAmount;
        }
        
        // making sure the shifted letters loop to beginning, or end, of alphabet
        let loopingAdjustment = 0;
        if (thisLetter > 96 && shiftedLetter > 122) {
            loopingAdjustment = shiftedLetter - 26;
        } else if (thisLetter > 96 && shiftedLetter < 96) {
            loopingAdjustment = shiftedLetter + 26;
        } else if (thisLetter < 91 && shiftedLetter > 90) {
            loopingAdjustment = shiftedLetter - 26;
        } else if (thisLetter < 91 && shiftedLetter < 65) {
           loopingAdjustment = shiftedLetter + 26;
        } else {
           loopingAdjustment = shiftedLetter;
        }

        let finalString = String.fromCharCode(loopingAdjustment);

        return finalString;


    });

    console.log(mappedLetters);

    return mappedLetters.join('');

}

module.exports = caesar

Answer 2

您在条件语句内声明了loopingAdjustment，其中let具有自己的作用域。在条件语句之外声明它，仅一次，并且仅在条件语句内更改其值。