base64编码和解码（JS）

var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
var base64DecodeChars = new Array(-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 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, -1, -1, -1, -1, -1, -1, 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, -1, -1, -1, -1, -1);
/**
 * base64编码
 * @param {Object} str
 */
function base64encode(str) {
    var out, i, len;
    var c1, c2, c3;
    len = str.length;
    i = 0;
    out = "";
    while(i < len) {
        c1 = str.charCodeAt(i++) & 0xff;
        if(i == len) {
            out += base64EncodeChars.charAt(c1 >> 2);
            out += base64EncodeChars.charAt((c1 & 0x3) << 4);
            out += "==";
            break;
        }
        c2 = str.charCodeAt(i++);
        if(i == len) {
            out += base64EncodeChars.charAt(c1 >> 2);
            out += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));
            out += base64EncodeChars.charAt((c2 & 0xF) << 2);
            out += "=";
            break;
        }
        c3 = str.charCodeAt(i++);
        out += base64EncodeChars.charAt(c1 >> 2);
        out += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4));
        out += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6));
        out += base64EncodeChars.charAt(c3 & 0x3F);
    }
    return out;
}
/**
 * base64解码
 * @param {Object} str
 */
function base64decode(str) {
    var c1, c2, c3, c4;
    var i, len, out;
    len = str.length;
    i = 0;
    out = "";
    while(i < len) {
        /* c1 */
        do {
            c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
        }
        while (i < len && c1 == -1);
        if(c1 == -1)
            break;
        /* c2 */
        do {
            c2 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
        }
        while (i < len && c2 == -1);
        if(c2 == -1)
            break;
        out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));
        /* c3 */
        do {
            c3 = str.charCodeAt(i++) & 0xff;
            if(c3 == 61)
                return out;
            c3 = base64DecodeChars[c3];
        }
        while (i < len && c3 == -1);
        if(c3 == -1)
            break;
        out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));
        /* c4 */
        do {
            c4 = str.charCodeAt(i++) & 0xff;
            if(c4 == 61)
                return out;
            c4 = base64DecodeChars[c4];
        }
        while (i < len && c4 == -1);
        if(c4 == -1)
            break;
        out += String.fromCharCode(((c3 & 0x03) << 6) | c4);
    }
    return out;
}