Question

I found this strange JavaScript I cannot understand. The for cycle has a strange syntax (many parameters), can you explain me how it is intended to work? Thanks

decode: function(s){
        for(var a, b, i = -1, l = (s = s.split("")).length, o = String.fromCharCode, c = "charCodeAt"; ++i < l;
            ((a = s[i][c](0)) & 0x80) &&
            (s[i] = (a & 0xfc) == 0xc0 && ((b = s[i + 1][c](0)) & 0xc0) == 0x80 ?
            o(((a & 0x03) << 6) + (b & 0x3f)) : o(128), s[++i] = "")
        );
        return s.join("");
    }

Answer 1

interesting function, apparently trans-coding a certain set of chars, kind of esoteric and will only work with an ASCII code but here’s the breakdown:

    for (var i = 0; i < s.length; i++) {
        var a = s.charCodeAt(i);

        if (a & 0x80) { // (a >= 128) if extended ascii

            var b = s.charCodeAt(i + 1);

            var specialA = (a & 0xfc) === 0xc0; // a IS [À, Á, Â or Ã] essentially [192, 193, 194, 195]
            var specialB = (b & 0xc0) === 0x80; // b >= 128 & b <= 191 eg. b is not a special Latin Ascii Letter

            if (specialA && specialB) {

                var txA = (a & 0x03) << 6; // [0, 64, 128, 192]
                var txB = b & 0x3f; // 0 - 63

                s[i] = String.fromCharCode(txA + txB);

            } else {
                s[i] = String.fromCharCode(128);
                s[++i] = "";
            }
        }
    }

hope this helps, either way i found the decoding interesting, reminds of reading raw assembler, lol -ck