title: Map multiple keys with lowdb
body: <p>In <a href="https://github.com/typicode/lowdb" rel="nofollow">lowdb</a> for Node.js, if I have a DB JSON like</p>
  
  <pre><code>[
      {
          "foo": "bar1",
          "tar": "ball1",
          "data": [
              {
                  "a": 1
              },
              {
                  "b": 2
              }
          ]
      },
      {
          "foo": "bar2",
          "tar": "ball2",
          "data": [
              {
                  "a": 1
              },
              {
                  "b": 2
              }
          ]
      }
  ]
  </code></pre>
  
  <p>I can get all foo's: <code>[bar1, bar2]</code> with the query <code>db.get('test').map('foo').value();</code></p>
  
  <p>However <strong>I need to get several keys</strong>, like if I could do something like <code>db.get('test').map(['foo', 'data.a']).value();</code> to get:</p>
  
  <pre><code>[
      {
          "foo": "bar1",
          "data": [
              {
                  "a": 1
              }
          ]
      },
      {
          "foo": "bar2",
          "data": [
              {
                  "a": 1
              }
          ]
      }
  ]
  </code></pre>
  
  <p><strong>How can I do this?</strong></p>