Javascript Base64 encode/decode

Base64.js

;"strict";

window.Base64 = {

    // private property
    _keyStr: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",

    // public method for encoding
    encode: function (input) {
        var output = "";
        var chr = [];
        var enc = [];
        var i = 0;

        input = Base64._utf8_encode(input);

        while (i < input.length) {

            chr[0] = input.charCodeAt(i++);
            chr[1] = input.charCodeAt(i++);
            chr[2] = input.charCodeAt(i++);

            enc[0] = chr[0] >> 2;
            enc[1] = ((chr[0] & 3) << 4) | (chr[1] >> 4);
            enc[2] = ((chr[1] & 15) << 2) | (chr[2] >> 6);
            enc[3] = chr[2] & 63;

            if (isNaN(chr[1])) {
                enc[2] = enc[3] = 64;
            } else if (isNaN(chr[2])) {
                enc[3] = 64;
            }

            output = output + this._keyStr.charAt(enc[0]) + this._keyStr.charAt(enc[1]) + this._keyStr.charAt(enc[2]) + this._keyStr.charAt(enc[3]);

        }

        return output;
    },

    // public method for decoding
    decode: function (input) {
        var output = "";
        var chr = [];
        var enc = [];
        var i = 0;

        input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");

        while (i < input.length) {

            enc[0] = this._keyStr.indexOf(input.charAt(i++));
            enc[1] = this._keyStr.indexOf(input.charAt(i++));
            enc[2] = this._keyStr.indexOf(input.charAt(i++));
            enc[3] = this._keyStr.indexOf(input.charAt(i++));

            chr[0] = (enc[0] << 2) | (enc[1] >> 4);
            chr[1] = ((enc[1] & 15) << 4) | (enc[2] >> 2);
            chr[2] = ((enc[2] & 3) << 6) | enc[3];

            output = output + String.fromCharCode(chr[0]);

            if (enc[2] != 64) {
                output = output + String.fromCharCode(chr[1]);
            }
            if (enc[3] != 64) {
                output = output + String.fromCharCode(chr[2]);
            }

        }

        output = Base64._utf8_decode(output);

        return output;

    },

    // private method for UTF-8 encoding
    _utf8_encode: function (string) {
        string = string.replace(/\r\n/g, "\n");
        var utftext = "";

        for (var n = 0; n < string.length; n++) {

            var c = string.charCodeAt(n);

            if (c < 128) {
                utftext += String.fromCharCode(c);
            } else if ((c > 127) && (c < 2048)) {
                utftext += String.fromCharCode((c >> 6) | 192);
                utftext += String.fromCharCode((c & 63) | 128);
            } else {
                utftext += String.fromCharCode((c >> 12) | 224);
                utftext += String.fromCharCode(((c >> 6) & 63) | 128);
                utftext += String.fromCharCode((c & 63) | 128);
            }

        }

        return utftext;
    },

    // private method for UTF-8 decoding
    _utf8_decode: function (utftext) {
        var string = "";
        var i  = 0;
        var c  = 0;
        var c1 = 0;
        var c2 = 0;

        while (i < utftext.length) {

            c = utftext.charCodeAt(i);

            if (c < 128) {
                string += String.fromCharCode(c);
                i++;
            } else if ((c > 191) && (c < 224)) {
                c2 = utftext.charCodeAt(i + 1);
                string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
                i += 2;
            } else {
                c2 = utftext.charCodeAt(i + 1);
                c3 = utftext.charCodeAt(i + 2);
                string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
                i += 3;
            }

        }

        return string;
    }
};

Basic tests

var stringTestValue = 'Text test';

console.assert(Base64.decode(Base64.encode(stringTestValue)) === stringTestValue);
console.assert(Base64.encode('Alpha') === "QWxwaGE=");
console.assert(Base64.encode('') === '' );
console.assert(Base64.encode(' ')  === "IA==");