taiwan-taxid-validator/dist/index.js

A validator for Taiwan uniform invoice numbers (統一發票號碼驗證器)

export default class TaxIdValidator {
    /**
     * 檢查發票號碼是否合法
     * @param invoiceId 發票號碼
     * @returns 是否合法
     */
    static isValid(invoiceId) {
        const checkKey = [1, 2, 1, 2, 1, 2, 4, 1];
        let isum = 0;
        let isum1 = 0;
        let isum2 = 0;
        if (invoiceId.length !== 8 || isNaN(Number(invoiceId))) {
            return false;
        }
        for (let i = 0; i < 8; i++) {
            const currentDigit = parseInt(invoiceId.charAt(i), 10);
            const product = checkKey[i] * currentDigit;
            const a = Math.floor(product / 10);
            const b = product % 10;
            if (i === 6 && invoiceId.charAt(6) === '7') {
                isum1 = isum + 1;
                isum2 = isum;
            }
            else {
                isum += a + b;
            }
        }
        if (invoiceId.charAt(6) === '7') {
            const lastDigit = parseInt(invoiceId.charAt(7), 10);
            const product = checkKey[7] * lastDigit;
            const a = Math.floor(product / 10);
            const b = product % 10;
            isum1 += a + b;
            isum2 += a + b;
            return (TaxIdValidator.isValidChecksum(isum1) ||
                TaxIdValidator.isValidChecksum(isum2));
        }
        return TaxIdValidator.isValidChecksum(isum);
    }
    static isValidChecksum(sum) {
        return sum - Math.round(sum / 5) * 5 === 0;
    }
}