JS Nested Merge

merged.js

function merged() {
  var mergeInto;

  [].forEach.call(arguments, function(obj, i) {
    if(i === 0) {
      mergeInto = obj;
    }
    else {
      Object.keys(obj).forEach(function(key) {
        var existing = mergeInto[key],
            value = obj[key];

        if(!existing || value.constructor != existing.constructor ||
           [Object, Array].indexOf(value.constructor) == -1) {
          mergeInto[key] = value;
        }
        else {
          if(value.constructor == Array) {
            existing.push.apply(existing, value);
          }
          else {
            mergeInto[key] = merged({}, existing, value);
          }
        }
      });
    }
  });

  return mergeInto;
}