编辑代码

//JSRUN引擎2.0，支持多达30种语言在线运行，全仿真在线交互输入输出。 
const base64abc = ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z", "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z", "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "+", "/"];

const base64codes = [255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 62, 255, 255, 255, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 255, 255, 255, 0, 255, 255, 255, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 255, 255, 255, 255, 255, 255, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51];

function getBase64Code(charCode) {
    if (charCode >= base64codes.length) {
        throw new Error("Unable to parse base64 string.");
    }
    const code = base64codes[charCode];
    if (code === 255) {
        throw new Error("Unable to parse base64 string.");
    }
    return code;
}

function bytesToBase64(bytes) {
    let result = '', i, l = bytes.length;
    for (i = 2; i < l; i += 3) {
        result += base64abc[bytes[i - 2] >> 2];
        result += base64abc[((bytes[i - 2] & 0x03) << 4) | (bytes[i - 1] >> 4)];
        result += base64abc[((bytes[i - 1] & 0x0F) << 2) | (bytes[i] >> 6)];
        result += base64abc[bytes[i] & 0x3F];
    }
    if (i === l + 1) {
        // 1 octet yet to write
        result += base64abc[bytes[i - 2] >> 2];
        result += base64abc[(bytes[i - 2] & 0x03) << 4];
        result += "==";
    }
    if (i === l) {
        // 2 octets yet to write
        result += base64abc[bytes[i - 2] >> 2];
        result += base64abc[((bytes[i - 2] & 0x03) << 4) | (bytes[i - 1] >> 4)];
        result += base64abc[(bytes[i - 1] & 0x0F) << 2];
        result += "=";
    }
    return result;
}

function base64ToBytes(str) {
    if (str.length % 4 !== 0) {
        throw new Error("Unable to parse base64 string.");
    }
    const index = str.indexOf("=");
    if (index !== -1 && index < str.length - 2) {
        throw new Error("Unable to parse base64 string.");
    }
    let missingOctets = str.endsWith("==") ? 2 : str.endsWith("=") ? 1 : 0, n = str.length, result = new Uint8Array(3 * (n / 4)), buffer;
    for (let i = 0, j = 0; i < n; i += 4,
    j += 3) {
        buffer = getBase64Code(str.charCodeAt(i)) << 18 | getBase64Code(str.charCodeAt(i + 1)) << 12 | getBase64Code(str.charCodeAt(i + 2)) << 6 | getBase64Code(str.charCodeAt(i + 3));
        result[j] = buffer >> 16;
        result[j + 1] = (buffer >> 8) & 0xFF;
        result[j + 2] = buffer & 0xFF;
    }
    return result.subarray(0, result.length - missingOctets);
}

function base64Encode(text) {
    return bytesToBase64(new TextEncoder().encode(text));
}

function base64Decode(text) {
    return (new TextDecoder()).decode(base64ToBytes(text));
}


console.log(base64Encode(123456));