Given 3 morse code characters determines the letter associated with it. Any of the morse can be substituted for ? and this code will respond with possibilities

morse-code-possibilities.js

function possibilities (signals) {
  var atoms = {
    ".": "E",
    "-": "T",
    "I": {
      ".": "S",
      "-": "U"
    },
    "A": {
      ".": "R",
      "-": "W"
    },
    "N": {
      ".": "D",
      "-": "K"
    },
    "M": {
      ".": "G",
      "-": "O"
    },
    "E": {
      ".": "I",
      "-": "A"
    },
    "T": {
      ".": "N",
      "-": "M"
    }
  };
  var chain = [];
  var tmp;
  signals = signals.split('');

  for (var i in signals) {
    var s = signals[i];
    
    if (i == 0) {
      if (s === '?') {
        chain.push(atoms['.']);
        chain.push(atoms['-'])
      } else {
        chain.push(atoms[s])
      }
    } else {
      tmp = chain.reduce((acc, l) => {
        if (s === '?') {
          acc.push(atoms[l]['-'])
          acc.push(atoms[l]['.'])
        } else {
          acc.push(atoms[l][s]);
        }

        return acc;
      }, [])

      chain = tmp;
    }
  }

  return chain;
}