Question: which combinations (with a maximum length of 4) are unused in international Morse code?

morse.js

// Question: which combinations with a maximum length of 4 are unused in international Morse code?
// http://en.wikipedia.org/wiki/Morse_code

var morseCodes = {
    '.-': 'A',
    '-...': 'B',
    '-.-.': 'C',
    '-..': 'D',
    '.': 'E',
    '..-.': 'F',
    '--.': 'G',
    '....': 'H',
    '..': 'I',
    '.---': 'J',
    '-.-': 'K',
    '.-..': 'L',
    '--': 'M',
    '-.': 'N',
    '---': 'O',
    '.--.': 'P',
    '--.-': 'Q',
    '.-.': 'R',
    '...': 'S',
    '-': 'T',
    '..-': 'U',
    '...-': 'V',
    '.--': 'W',
    '-..-': 'X',
    '-.--': 'Y',
    '--..': 'Z'
};

// Note: 4-signal Morse codes are more than 4 bit.
// With 4 signals (dot or dash), you get 30 combinations:
// 2 (length 1) + 4 (length 2) + 8 (length 3) + 16 (length 4)
var maxLen = 4;
for(var len = 1; len <= maxLen; len++) {
    var combinations = Math.pow(2, len);
    for(var x = 0; x < combinations; x++) {
        var binary = x.toString(2);
        // pad with zeros
        while(binary.length < len) {
            binary = '0' + binary;
        }
        // To replace multiple times, we need a regular expression
        var code = binary.replace(/0/g, '.').replace(/1/g, '-');
        var used = (code in morseCodes ? '' : ' UNUSED');
        console.log(code+used);
    }
}