title: How to get previous value of <select> in React?
body: <p>An example.</p>
  
  <p><code>red</code> is selected from the very start.</p>
  
  <p>Then I select <code>green</code>. That is, from <code>red</code> to <code>green</code>.</p>
  
  <p>I can get new value <code>green</code> in <code>event.currentTarget.value</code>. But how do I get previous <code>red</code>?</p>
  
  <pre><code>&lt;select className="foo" onChange={this.onSectChange} value="red"&gt;
      &lt;option value="no color"&gt;No Color&lt;/option&gt;
      &lt;option value="red"&gt;Red&lt;/option&gt;  // this one is selected
      &lt;option value="green"&gt;Green&lt;/option&gt; // this one I will select
      &lt;option value="blue"&gt;Blue&lt;/option&gt;
  &lt;/select&gt;
  
  onSectChange = (event) =&gt; {
  
      let prevVal = event.??? // How to get a previous value, that is Red
      let newVal = event.currentTarget.value; // Green - is a new value just selected, not previous
  
  }
  </code></pre>
  
  <p>I mean, does React provide this functionality out-of-the-box along with their <code>SyntheticEvent</code> creation? Or do I still have to hack to get it?</p>