encodebase64 七牛上传base64文件时 encodedkey 时会用到

  encode64(input) {
            var keyStr = "ABCDEFGHIJKLMNOP" +
                        "QRSTUVWXYZabcdef" +
                        "ghijklmnopqrstuv" +
                        "wxyz0123456789+/" +
                        "=";
            input = escape(input);//注意escape（）函数
            var output = "";
            var chr1, chr2, chr3 = "";
            var enc1, enc2, enc3, enc4 = "";
            var i = 0;
            do {
            chr1 = input.charCodeAt(i++);
            chr2 = input.charCodeAt(i++);
            chr3 = input.charCodeAt(i++);
            enc1 = chr1 >> 2;
            enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
            enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
            enc4 = chr3 & 63;
            if (isNaN(chr2)) {
            enc3 = enc4 = 64;
            } else if (isNaN(chr3)) {
            enc4 = 64;
            }
            output = output +
            keyStr.charAt(enc1) +
            keyStr.charAt(enc2) +
            keyStr.charAt(enc3) +
            keyStr.charAt(enc4);
            chr1 = chr2 = chr3 = "";
            enc1 = enc2 = enc3 = enc4 = "";
            } while (i < input.length);
            return output;
        }