_merge.js

var arrayShift = [].shift;

function _deep_merge (dest, src) {
  if( typeof dest !== typeof src ) {
    return src;
  }
  if( src instanceof Array ) {
    [].push.apply(dest, src);
    return dest;
  }
  if( typeof src === 'object' ) {
    for( var key in src ) {
      dest[key] = _deep_merge(dest[key], src[key]);
    }
    return dest;
  }
  return src;
}

function _merge () {
    var dest = arrayShift.call(arguments),
        src = arrayShift.call(arguments);

    while( src ) {
      dest = _deep_merge(dest, src);
      src = arrayShift.call(arguments);
    }

    return dest;
}