index.mjs

const basicTable = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
/**
 * create index map
 *
 * @param table base62 string table
 */
function createIndexMap(table = basicTable) {
    return table
        .split('')
        .reduce(function (result, value, index) {
        result[value] = index;
        return result;
    }, {});
}
const basicIndexMap = createIndexMap();
/**
 * decode to decimal number from base62 string
 *
 * @param str base62 string
 * @param [baseTable=basicTable] base62 table
 * @throws {TypeError} str is not a string
 * @throws {Error} str is unexpected format
 * @throws {Error} baseTable is not 62 in length
 */
function decode(str, baseTable = basicTable) {
    if (typeof str !== 'string') {
        throw new TypeError(`str must be a string: ${str}`);
    }
    if (!/^-?[\dA-Za-z]+$/.test(str)) {
        throw new Error(`unexpected format: ${str}`);
    }
    if (baseTable.length !== 62) {
        throw new Error('baseTable must be 62 in length');
    }
    const indexMap = baseTable === basicTable ? basicIndexMap : createIndexMap(baseTable);
    const isNegative = str[0] === '-';
    const numbers = (isNegative ? str.slice(1) : str).split('');
    const numbersLength = numbers.length;
    const result = numbers.reduce(function (result, n, index) {
        return result + indexMap[n] * Math.pow(62, numbersLength - index - 1);
    }, 0);
    return isNegative ? -result : result;
}
/**
 * encode to base62 string from number
 *
 * @param num integer
 * @param [baseTable=basicTable] base62 table
 * @throws {TypeError} num is not an Integer
 * @throws {Error} baseTable is not 62 in length
 */
function encode(num, baseTable = basicTable) {
    if (!Number.isSafeInteger(num)) {
        throw new TypeError(`num is must be an integer: ${num}`);
    }
    if (baseTable.length !== 62) {
        throw new Error('baseTable must be 62 in length');
    }
    if (num === 0) {
        return '0';
    }
    const result = [];
    let n = Math.abs(num);
    while (n > 0) {
        result.unshift(baseTable[n % 62]);
        n = Math.floor(n / 62);
    }
    return num < 0 ? `-${result.join('')}` : result.join('');
}

export { decode, encode };