JS转TS函数报错：代码路径未返回值与类型索引问题求修复

我把一个用于过滤国家数据的JavaScript函数转换为TypeScript后遇到两个错误，无法自行修复，原代码如下：

const countryData = [
    {
        id: 1,
        name: 'Afghanistan',
        isoAlpha2: 'AF',
        isoAlpha3: 'AFG',
        isoNumeric: 4,
        currency: {
            code: 'AFN',
            name: 'Afghani',
            symbol: '؋'
        },
        flag: "flasg",
        callingCodes: ['+93'],
        languages: ['pus'],
        emoji: '🇦🇫'
    },
    {
        id: 2,
        name: 'Albania',
        isoAlpha2: 'AL',
        isoAlpha3: 'ALB',
        isoNumeric: 8,
        currency: {
            code: 'ALL',
            name: 'Lek',
            symbol: 'L'
        },
        flag: "flasg",
        callingCodes: ['+355'],
        languages: ['sqi'],
        emoji: '🇦🇱'
    }
]

export interface CountryDataTypes {
    id: number;
    name: string;
    isoAlpha2: string;
    isoAlpha3: string;
    isoNumeric: number;
    currency: {
        code: string;
        name: string;
        symbol: string | boolean;
    }
    flag: string;
    callingCodes: string[];
    languages: string[];
    emoji: string;
}
interface Props {
    name?: string;
    countryCode?: string;
    callingCode?: string;
    currencyName?: string;
    currencyCode?: string;
    currencySymbol?: string;
    isoNumeric?: number;
}

export function lookup(data: Props): CountryDataTypes {
    const fields = Object.entries(data)
    const result = countryData.find((d) => { // Error 1
        for (var key in fields) {
            return d[fields[key][0]] === fields[key][1] //Error 2
        }
    })
    return result as CountryDataTypes || {} as CountryDataTypes;
}

遇到的错误：

• 错误1：Not all code paths return a value.（并非所有代码路径都返回值）
• 错误2：Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{ id: number; name: string; ... }'. No index signature with a parameter of type 'string' was found on type '{ id: number; name: string; ... }'.（元素隐式具有'any'类型，因为字符串类型的表达式无法用于索引指定类型，未找到对应索引签名）

错误修复方案 #

修复错误1：补全返回逻辑并修正循环逻辑

原find回调函数存在两个问题：一是当fields为空时，循环不执行导致无返回值；二是当前循环会在第一个字段比对后直接返回，无法实现所有传入字段都匹配的过滤需求。需要调整为：遍历所有字段，只要有一个不匹配就返回false，全部匹配完后返回true。

修复错误2：字段映射与类型断言

Props中的字段名和CountryDataTypes的字段名不完全对应（比如countryCode对应isoAlpha2，currencyName对应currency.name），需要先做字段映射，再通过keyof类型断言告诉TypeScript索引的合法性，消除类型报错。

完整修复后的代码 #

const countryData: CountryDataTypes[] = [
    {
        id: 1,
        name: 'Afghanistan',
        isoAlpha2: 'AF',
        isoAlpha3: 'AFG',
        isoNumeric: 4,
        currency: {
            code: 'AFN',
            name: 'Afghani',
            symbol: '؋'
        },
        flag: "flasg",
        callingCodes: ['+93'],
        languages: ['pus'],
        emoji: '🇦🇫'
    },
    {
        id: 2,
        name: 'Albania',
        isoAlpha2: 'AL',
        isoAlpha3: 'ALB',
        isoNumeric: 8,
        currency: {
            code: 'ALL',
            name: 'Lek',
            symbol: 'L'
        },
        flag: "flasg",
        callingCodes: ['+355'],
        languages: ['sqi'],
        emoji: '🇦🇱'
    }
]

export interface CountryDataTypes {
    id: number;
    name: string;
    isoAlpha2: string;
    isoAlpha3: string;
    isoNumeric: number;
    currency: {
        code: string;
        name: string;
        symbol: string | boolean;
    }
    flag: string;
    callingCodes: string[];
    languages: string[];
    emoji: string;
}

interface Props {
    name?: string;
    countryCode?: string;
    callingCode?: string;
    currencyName?: string;
    currencyCode?: string;
    currencySymbol?: string;
    isoNumeric?: number;
}

export function lookup(data: Props): CountryDataTypes {
    const fields = Object.entries(data)
    const result = countryData.find((d) => {
        for (const [key, value] of fields) {
            let compareValue: unknown;
            // 处理字段映射
            switch (key) {
                case 'countryCode':
                    compareValue = d.isoAlpha2;
                    break;
                case 'callingCode':
                    compareValue = d.callingCodes[0];
                    break;
                case 'currencyName':
                    compareValue = d.currency.name;
                    break;
                case 'currencyCode':
                    compareValue = d.currency.code;
                    break;
                case 'currencySymbol':
                    compareValue = d.currency.symbol;
                    break;
                default:
                    compareValue = d[key as keyof CountryDataTypes];
                    break;
            }
            if (compareValue !== value) {
                return false;
            }
        }
        return true;
    })
    return result ?? ({} as CountryDataTypes);
}

内容的提问来源于stack exchange，提问作者Simon Santana