WinJS Base64编码和解码 metro

之前用纯JS编码和解码字符串，因为字符串大小为2M多，所以效率相当慢，得两三秒。

之后改为了用windos api编码解码，效率一下提高，基本没有延迟的感觉。

metro下的Javascript base64编码：

var Base64 = {
    //编码
    encode: function (input) {
        var output = "";
        var buffer = Windows.Security.Cryptography.CryptographicBuffer.convertStringToBinary(input,"utf8");//字符串转缓存
        output = Windows.Security.Cryptography.CryptographicBuffer.encodeToBase64String(buffer);//将缓存编码，返回编码后的字符串
        return output;
    },
    //解码
    decode: function (input) {
        var output = "";
        var buffer = Windows.Security.Cryptography.CryptographicBuffer.decodeFromBase64String(input);//将base64解码为缓存
        output = Windows.Security.Cryptography.CryptographicBuffer.convertBinaryToString("utf8", buffer);//将缓存转为字符串
        return output;

    }

}