jmeas/namespace-diff.js

function buildOutput(outStates, base, sep) {
  for (var j = 0; j < outStates.length; j++) {
    outStates[j] = (base += outStates[j]);
    if (j !== outStates.length) {
      base += sep;
    }
  }
  return outStates;
}

function namespaceDiff(start, end, sep = '.') {

  // If the states are the same, then we bail out
  if (start === end) {
    return { outStates: [], inStates: [] };
  }

  // If there's no end, then we don't go anywhere
  if (typeof end === 'undefined') {
    return { outStates: [], inStates: [] };
  }

  // If the start doesn't exist, then we enter into
  // our states without any exits.
  if (typeof start === 'undefined') {
    var output = buildOutput(end.split(sep), '', sep);
    if (end !== '') {
      output.unshift('');
    }
    return { outStates: [], inStates: output };
  }

  // Assuming we're working with empty strings from now on
  // makes future calculations easier
  start = start ? start : '';
  end = end ? end : '';

  // Determine the state up to which they are the same
  var startStates = start ? start.split(sep) : [];
  var endStates = end ? end.split(sep) : [];
  var base = '';
  for (var i = 0; i < startStates.length; i++) {
    if (startStates[i] !== endStates[i]) {
      break;
    } else {
      base += startStates[i] + sep;
    }
  }

  // Use that information to generate the result
  return {
    outStates: buildOutput(startStates.slice(i), base, sep).reverse(),
    inStates: buildOutput(endStates.slice(i), base, sep)
  };
}

export default namespaceDiff;