Here is a method to read "malformed", it attempts to do readString on it, if it errors then it tries to read it in another way, so this is an alternative to readStringReplaceMalformed, it is an attempt at readingMalformed

function readAsChar8ThenAsChar16(stringPtr, known_len, jschar) {
    // when reading as jschar it assumes max length of 500

    // stringPtr is either char or jschar, if you know its jschar for sure, pass 2nd arg as true
    // if known_len is passed, then assumption is not made, at the known_len position in array we will see a null char
    // i tried getting known_len from stringPtr but its not possible, it has be known, i tried this:
        //"stringPtr.contents.toString()" "95"
        //"stringPtr.toString()" "ctypes.unsigned_char.ptr(ctypes.UInt64("0x7f73d5c87650"))"
        // so as we see neither of these is 77, this is for the example of "_scratchpad/EnTeHandle.js at master · Noitidart/_scratchpad - Mozilla Firefox"

    // tries to do read string on stringPtr, if it fails then it falls to read as jschar

    var readJSCharString = function() {
        var assumption_max_len = known_len ? known_len : 500;
        var ptrAsArr = ctypes.cast(stringPtr, ctypes.unsigned_char.array(assumption_max_len).ptr).contents; // MUST cast to unsigned char (not ctypes.jschar, or ctypes.char) as otherwise i dont get foreign characters, as they are got as negative values, and i should read till i find a 0 which is null terminator which will have unsigned_char code of 0 // can test this by reading a string like this: "_scratchpad/EnTeHandle.js at master · Noitidart/_scratchpad - Mozilla Firefox" at js array position 36 (so 37 if count from 1), we see 183, and at 77 we see char code of 0 IF casted to unsigned_char, if casted to char we see -73 at pos 36 but pos 77 still 0, if casted to jschar we see chineese characters in all spots expect spaces even null terminator is a chineese character
        console.info('ptrAsArr.length:', ptrAsArr.length);
        //console.log('debug-msg :: dataCasted:', dataCasted, uneval(dataCasted), dataCasted.toString());
        var charCode = [];
        var fromCharCode = []
        for (var i=0; i<ptrAsArr.length; i++) { //if known_len is correct, then will not hit null terminator so like in example of "_scratchpad/EnTeHandle.js at master · Noitidart/_scratchpad - Mozilla Firefox" if you pass length of 77, then null term will not get hit by this loop as null term is at pos 77 and we go till `< known_len`
            var thisUnsignedCharCode = ptrAsArr.addressOfElement(i).contents;
            if (thisUnsignedCharCode == 0) {
                // reached null terminator, break
                console.log('reached null terminator, at pos: ', i);
                break;
            }
            charCode.push(thisUnsignedCharCode);
            fromCharCode.push(String.fromCharCode(thisUnsignedCharCode));
        }
        console.info('charCode:', charCode);
        console.info('fromCharCode:', fromCharCode);
        var char16_val = fromCharCode.join('');
        console.info('char16_val:', char16_val);
        return char16_val;
    }

    if (!jschar) {
        try {
            var char8_val = stringPtr.readString();
            console.info('stringPtr.readString():', char8_val);
            return char8_val;
        } catch (ex if ex.message.indexOf('malformed UTF-8 character sequence at offset ') == 0) {
            console.warn('ex of offset utf8 read error when trying to do readString so using alternative method, ex:', ex);
            return readJSCharString();
        }
    } else {
        return readJSCharString();
    }
}