js Base64

Base64.js代码如下：

//
// THIS FILE IS AUTOMATICALLY GENERATED! DO NOT EDIT BY HAND!
//
;(function(global, factory) {
    typeof exports === 'object' && typeof module !== 'undefined'
        ? module.exports = factory()
        : typeof define === 'function' && define.amd
        ? define(factory) :
        // cf. https://github.com/dankogai/js-base64/issues/119
        (function() {
            // existing version for noConflict()
            const _Base64 = global.Base64;
            const gBase64 = factory();
            gBase64.noConflict = () => {
                global.Base64 = _Base64;
                return gBase64;
            };
            if (global.Meteor) { // Meteor.js
                Base64 = gBase64;
            }
            global.Base64 = gBase64;
        })();
}((typeof self !== 'undefined' ? self
        : typeof window !== 'undefined' ? window
        : typeof global !== 'undefined' ? global
        : this
), function() {
    'use strict';

/**
 *  base64.ts
 *
 *  Licensed under the BSD 3-Clause License.
 *    http://opensource.org/licenses/BSD-3-Clause
 *
 *  References:
 *    http://en.wikipedia.org/wiki/Base64
 *
 * @author Dan Kogai (https://github.com/dankogai)
 */
const version = '3.6.0';
/**
 * @deprecated use lowercase `version`.
 */
const VERSION = version;
const _hasatob = typeof atob === 'function';
const _hasbtoa = typeof btoa === 'function';
const _hasBuffer = typeof Buffer === 'function';
const _TD = typeof TextDecoder === 'function' ? new TextDecoder() : undefined;
const _TE = typeof TextEncoder === 'function' ? new TextEncoder() : undefined;
const b64ch = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
const b64chs = [...b64ch];
const b64tab = ((a) => {
    let tab = {};
    a.forEach((c, i) => tab[c] = i);
    return tab;
})(b64chs);
const b64re = /^(?:[A-Za-zd+/]{4})*?(?:[A-Za-zd+/]{2}(?:==)?|[A-Za-zd+/]{3}=?)?$/;
const _fromCC = String.fromCharCode.bind(String);
const _U8Afrom = typeof Uint8Array.from === 'function'
    ? Uint8Array.from.bind(Uint8Array)
    : (it, fn = (x) => x) => new Uint8Array(Array.prototype.slice.call(it, 0).map(fn));
const _mkUriSafe = (src) => src
    .replace(/[+/]/g, (m0) => m0 == '+' ? '-' : '_')
    .replace(/=+$/m, '');
const _tidyB64 = (s) => s.replace(/[^A-Za-z0-9+/]/g, '');
/**
 * polyfill version of `btoa`
 */
const btoaPolyfill = (bin) => {
    // console.log('polyfilled');
    let u32, c0, c1, c2, asc = '';
    const pad = bin.length % 3;
    for (let i = 0; i < bin.length;) {
        if ((c0 = bin.charCodeAt(i++)) > 255 ||
            (c1 = bin.charCodeAt(i++)) > 255 ||
            (c2 = bin.charCodeAt(i++)) > 255)
            throw new TypeError('invalid character found');
        u32 = (c0 << 16) | (c1 << 8) | c2;
        asc += b64chs[u32 >> 18 & 63]
            + b64chs[u32 >> 12 & 63]
            + b64chs[u32 >> 6 & 63]
            + b64chs[u32 & 63];
    }
    return pad ? asc.slice(0, pad - 3) + "===".substring(pad) : asc;
};
/**
 * does what `window.btoa` of web browsers do.
 * @param {String} bin binary string
 * @returns {string} Base64-encoded string
 */
const _btoa = _hasbtoa ? (bin) => btoa(bin)
    : _hasBuffer ? (bin) => Buffer.from(bin, 'binary').toString('base64')
        : btoaPolyfill;
const _fromUint8Array = _hasBuffer
    ? (u8a) => Buffer.from(u8a).toString('base64')
    : (u8a) => {
        // cf. https://stackoverflow.com/questions/12710001/how-to-convert-uint8-array-to-base64-encoded-string/12713326#12713326
        const maxargs = 0x1000;
        let strs = [];
        for (let i = 0, l = u8a.length; i < l; i += maxargs) {
            strs.push(_fromCC.apply(null, u8a.subarray(i, i + maxargs)));
        }
        return _btoa(strs.join(''));
    };
/**
 * converts a Uint8Array to a Base64 string.
 * @param {boolean} [urlsafe] URL-and-filename-safe a la RFC4648 §5
 * @returns {string} Base64 string
 */
const fromUint8Array = (u8a, urlsafe = false) => urlsafe ? _mkUriSafe(_fromUint8Array(u8a)) : _fromUint8Array(u8a);
// This trick is found broken https://github.com/dankogai/js-base64/issues/130
// const utob = (src: string) => unescape(encodeURIComponent(src));
// reverting good old fationed regexp
const cb_utob = (c) => {
    if (c.length < 2) {
        var cc = c.charCodeAt(0);
        return cc < 0x80 ? c
            : cc < 0x800 ? (_fromCC(0xc0 | (cc >>> 6))
                + _fromCC(0x80 | (cc & 0x3f)))
                : (_fromCC(0xe0 | ((cc >>> 12) & 0x0f))
                    + _fromCC(0x80 | ((cc >>> 6) & 0x3f))
                    + _fromCC(0x80 | (cc & 0x3f)));
    }
    else {
        var cc = 0x10000
            + (c.charCodeAt(0) - 0xD800) * 0x400
            + (c.charCodeAt(1) - 0xDC00);
        return (_fromCC(0xf0 | ((cc >>> 18) & 0x07))
            + _fromCC(0x80 | ((cc >>> 12) & 0x3f))
            + _fromCC(0x80 | ((cc >>> 6) & 0x3f))
            + _fromCC(0x80 | (cc & 0x3f)));
    }
};
const re_utob = /[uD800-uDBFF][uDC00-uDFFFF]|[^x00-x7F]/g;
/**
 * @deprecated should have been internal use only.
 * @param {string} src UTF-8 string
 * @returns {string} UTF-16 string
 */
const utob = (u) => u.replace(re_utob, cb_utob);
//
const _encode = _hasBuffer
    ? (s) => Buffer.from(s, 'utf8').toString('base64')
    : _TE
        ? (s) => _fromUint8Array(_TE.encode(s))
        : (s) => _btoa(utob(s));
/**
 * converts a UTF-8-encoded string to a Base64 string.
 * @param {boolean} [urlsafe] if `true` make the result URL-safe
 * @returns {string} Base64 string
 */
const encode = (src, urlsafe = false) => urlsafe
    ? _mkUriSafe(_encode(src))
    : _encode(src);
/**
 * converts a UTF-8-encoded string to URL-safe Base64 RFC4648 §5.
 * @returns {string} Base64 string
 */
const encodeURI = (src) => encode(src, true);
// This trick is found broken https://github.com/dankogai/js-base64/issues/130
// const btou = (src: string) => decodeURIComponent(escape(src));
// reverting good old fationed regexp
const re_btou = /[xC0-xDF][x80-xBF]|[xE0-xEF][x80-xBF]{2}|[xF0-xF7][x80-xBF]{3}/g;
const cb_btou = (cccc) => {
    switch (cccc.length) {
        case 4:
            var cp = ((0x07 & cccc.charCodeAt(0)) << 18)
                | ((0x3f & cccc.charCodeAt(1)) << 12)
                | ((0x3f & cccc.charCodeAt(2)) << 6)
                | (0x3f & cccc.charCodeAt(3)), offset = cp - 0x10000;
            return (_fromCC((offset >>> 10) + 0xD800)
                + _fromCC((offset & 0x3FF) + 0xDC00));
        case 3:
            return _fromCC(((0x0f & cccc.charCodeAt(0)) << 12)
                | ((0x3f & cccc.charCodeAt(1)) << 6)
                | (0x3f & cccc.charCodeAt(2)));
        default:
            return _fromCC(((0x1f & cccc.charCodeAt(0)) << 6)
                | (0x3f & cccc.charCodeAt(1)));
    }
};
/**
 * @deprecated should have been internal use only.
 * @param {string} src UTF-16 string
 * @returns {string} UTF-8 string
 */
const btou = (b) => b.replace(re_btou, cb_btou);
/**
 * polyfill version of `atob`
 */
const atobPolyfill = (asc) => {
    // console.log('polyfilled');
    asc = asc.replace(/s+/g, '');
    if (!b64re.test(asc))
        throw new TypeError('malformed base64.');
    asc += '=='.slice(2 - (asc.length & 3));
    let u24, bin = '', r1, r2;
    for (let i = 0; i < asc.length;) {
        u24 = b64tab[asc.charAt(i++)] << 18
            | b64tab[asc.charAt(i++)] << 12
            | (r1 = b64tab[asc.charAt(i++)]) << 6
            | (r2 = b64tab[asc.charAt(i++)]);
        bin += r1 === 64 ? _fromCC(u24 >> 16 & 255)
            : r2 === 64 ? _fromCC(u24 >> 16 & 255, u24 >> 8 & 255)
                : _fromCC(u24 >> 16 & 255, u24 >> 8 & 255, u24 & 255);
    }
    return bin;
};
/**
 * does what `window.atob` of web browsers do.
 * @param {String} asc Base64-encoded string
 * @returns {string} binary string
 */
const _atob = _hasatob ? (asc) => atob(_tidyB64(asc))
    : _hasBuffer ? (asc) => Buffer.from(asc, 'base64').toString('binary')
        : atobPolyfill;
//
const _toUint8Array = _hasBuffer
    ? (a) => _U8Afrom(Buffer.from(a, 'base64'))
    : (a) => _U8Afrom(_atob(a), c => c.charCodeAt(0));
/**
 * converts a Base64 string to a Uint8Array.
 */
const toUint8Array = (a) => _toUint8Array(_unURI(a));
//
const _decode = _hasBuffer
    ? (a) => Buffer.from(a, 'base64').toString('utf8')
    : _TD
        ? (a) => _TD.decode(_toUint8Array(a))
        : (a) => btou(_atob(a));
const _unURI = (a) => _tidyB64(a.replace(/[-_]/g, (m0) => m0 == '-' ? '+' : '/'));
/**
 * converts a Base64 string to a UTF-8 string.
 * @param {String} src Base64 string.  Both normal and URL-safe are supported
 * @returns {string} UTF-8 string
 */
const decode = (src) => _decode(_unURI(src));
/**
 * check if a value is a valid Base64 string
 * @param {String} src a value to check
  */
const isValid = (src) => {
    if (typeof src !== 'string')
        return false;
    const s = src.replace(/s+/g, '').replace(/=+$/, '');
    return !/[^s0-9a-zA-Z+/]/.test(s) || !/[^s0-9a-zA-Z-_]/.test(s);
};
//
const _noEnum = (v) => {
    return {
        value: v, enumerable: false, writable: true, configurable: true
    };
};
/**
 * extend String.prototype with relevant methods
 */
const extendString = function () {
    const _add = (name, body) => Object.defineProperty(String.prototype, name, _noEnum(body));
    _add('fromBase64', function () { return decode(this); });
    _add('toBase64', function (urlsafe) { return encode(this, urlsafe); });
    _add('toBase64URI', function () { return encode(this, true); });
    _add('toBase64URL', function () { return encode(this, true); });
    _add('toUint8Array', function () { return toUint8Array(this); });
};
/**
 * extend Uint8Array.prototype with relevant methods
 */
const extendUint8Array = function () {
    const _add = (name, body) => Object.defineProperty(Uint8Array.prototype, name, _noEnum(body));
    _add('toBase64', function (urlsafe) { return fromUint8Array(this, urlsafe); });
    _add('toBase64URI', function () { return fromUint8Array(this, true); });
    _add('toBase64URL', function () { return fromUint8Array(this, true); });
};
/**
 * extend Builtin prototypes with relevant methods
 */
const extendBuiltins = () => {
    extendString();
    extendUint8Array();
};
const gBase64 = {
    version: version,
    VERSION: VERSION,
    atob: _atob,
    atobPolyfill: atobPolyfill,
    btoa: _btoa,
    btoaPolyfill: btoaPolyfill,
    fromBase64: decode,
    toBase64: encode,
    encode: encode,
    encodeURI: encodeURI,
    encodeURL: encodeURI,
    utob: utob,
    btou: btou,
    decode: decode,
    isValid: isValid,
    fromUint8Array: fromUint8Array,
    toUint8Array: toUint8Array,
    extendString: extendString,
    extendUint8Array: extendUint8Array,
    extendBuiltins: extendBuiltins,
};

    //
    // export Base64 to the namespace
    //
    // ES5 is yet to have Object.assign() that may make transpilers unhappy.
    // gBase64.Base64 = Object.assign({}, gBase64);
    gBase64.Base64 = {};
    Object.keys(gBase64).forEach(k => gBase64.Base64[k] = gBase64[k]);
    return gBase64;
}));

从IE10+浏览器开始，所有浏览器就原生提供了Base64编码、解码方法，不仅可以用于浏览器环境，Service Worker环境也可以使用。
方法名就是 atob 和 btoa ，具体语法如下：

window.btoa('china is so nb') // 编码
"Y2hpbmEgaXMgc28gbmI="
window.atob("Y2hpbmEgaXMgc28gbmI=") // 解码
"china is so nb"

IE8/IE9的polyfill
  当下，仍有不少PC项目还需要兼容IE9，所以，我们可以专门针对这些浏览器再引入一段ployfill脚本或者一个JS文件即可。

[if IE] 表示所有IE浏览器，由于IE10+浏览器已经放弃了著名的IE条件注释的支持，Chrome等浏览器本身就不支持这个IE私有语法，因此，很天然的，上面一段script引入只在IE9-浏览器下有效。而我们本来就希望只IE8，IE9浏览器引入ployfill，于是正好完美衔接上。

也就是原生支持atob和btoa方法的浏览器认为就是一段无需关心的HTML注释，不支持atob和btoa的IE9及其以下浏览器则会加载我们的base64-polyfill.js，使浏览器也支持 window.btoa 和 window.atob 这个语法。

开源的base64.js ，使用很简单，浏览器引入该JS文件，然后Base64编码这样：

Base64.encode('china is so nb'); // 编码
"Y2hpbmEgaXMgc28gbmI="

解码就调用 decode方法，如下：

Base64.decode("Y2hpbmEgaXMgc28gbmI="); // 解码
'china is so nb'