Javascript“声明但从未使用过的变量”......即使我正在使用它？答案

【问题标题】：Javascript "variable declared but never used"... even though I'm using it?Javascript“声明但从未使用过的变量”......即使我正在使用它？
【发布时间】：2020-10-10 21:16:36
【问题描述】：

我一定是错过了什么。

在下面的代码中，我清楚地声明了loopingAdjustment，然后在它的正下方，我在fromCharCode 函数中调用它。所以，我正在使用它，对吧？我应该可以调用它，因为它在同一个范围内，对吧？

为什么 VSCode 说它“从未使用过”，为什么我的终端说它“未定义”？

谢谢。

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

【问题讨论】：

标签： javascript arrays function variables scope

【解决方案1】：

您在条件语句中声明 loopingAdjustment，其中 let 有自己的范围。在条件句之外声明它，仅在条件句中更改其值一次。

【讨论】：

【解决方案2】：

这是因为范围而发生的，因为您仅在 if 语句中声明和定义了 loopingAdjustment 变量，因此范围仅限于 if 语句。要解决此问题，您可以在 if 之外声明 loopingAdjustment 并在 if 语句中分配它。您可以从下面的代码中获取参考，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

【讨论】：

哇，谢谢。不敢相信我花了这么长时间才尝试在 if 语句中声明并在外部使用它。