title: Combine multiple arrays by same key
body: <p>I'm trying combine multiple arrays by a specific <code>key</code> property. For example, I have </p>
  
  <p><strong>arr1</strong></p>
  
  <pre><code>  [{
      key: 'A',
      items: [{name: 'a item'}]
    }, {
      key: 'B',
      items: [{name: 'b item'}]
    }]
  </code></pre>
  
  <p><strong>arr2</strong></p>
  
  <pre><code>  [{
      key: 'B',
      items: [{name: 'another b item'}, {name: 'more b items'}, {name: 'even more b items'}]
    }]
  </code></pre>
  
  <p>How do I produce the following <strong>arr3</strong>?</p>
  
  <pre><code>  [{
      key: 'A',
      items: [{name: 'a item'}]
    },
    {
      key: 'B',
      items: [{name: 'b item'}, {name: 'another b item'}, {name: 'more b items'}, {name: 'even more b items'}]
    }]
  </code></pre>