Javascript实现Base64解码

工作中需要用到，在stackoverflow中找到的，实践证明可用。

function decode_base64(s) {
    var e = {}, i, k, v = [],
        r = '',
        w = String.fromCharCode;
    var n = [
        [65, 91],
        [97, 123],
        [48, 58],
        [43, 44],
        [47, 48]
    ];

    for (z in n) {
        for (i = n[z][0]; i < n[z][1]; i++) {
            v.push(w(i));
        }
    }
    for (i = 0; i < 64; i++) {
        e[v[i]] = i;
    }

    for (i = 0; i < s.length; i += 72) {
        var b = 0,
            c, x, l = 0,
            o = s.substring(i, i + 72);
        for (x = 0; x < o.length; x++) {
            c = e[o.charAt(x)];
            b = (b << 6) + c;
            l += 6;
            while (l >= 8) {
                r += w((b >>> (l -= 8)) % 256);
            }
        }
    }
    return r;
}