title: Append key/value pair to object
body: <p>So, I have</p>
  
  <pre><code>{
    'A': {
      'B': 1
    },
    'B': {
      'A': 1
    }
  }
  </code></pre>
  
  <p>And now I need to add more keys into 'B' so it would output</p>
  
  <pre><code>{
    'A': {
      'B': 1
    },
    'B': {
      'A': 1,
      'C': 2,
      'D': 4
    }
  }
  </code></pre>
  
  <p>The final result needs to be a similar object and not an array. Obviously .push(), .splice, etc, does not work.</p>
  
  <p>How do I do this?</p>