title: React idiomatic way to update Map object in state
body: <p>I'm using the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map" rel="noreferrer">Map</a> class.</p>
  
  <p>I have a state like this:</p>
  
  <pre><code>{
      rows: new Map([])
  }
  </code></pre>
  
  <p>With each row representing an entry in a table.
  I'd like to update each row independently and asynchronously in a thread-safe manner.</p>
  
  <p>What is the idiomatic React way to perform a setState when each modification is something like this (assume "fooId" has already been inserted into the Map):</p>
  
  <pre><code>const rows = this.state.rows;
  const row = rows.get("fooId");
  row.status = '75%';
  
  this.setState({
      rows: rows
  });
  </code></pre>