title: Do I need "...this.state" when calling this.setState()
body: <p>I can't seem to find a consistent example of how to properly set state in React.</p>
  
  <p>Say, I've got my component that has the state:</p>
  
  <pre><code>state = {
     propertyOne: 'abc',
     propertyTwo: 'def',
     propertyThree: 'ghi',
  }
  </code></pre>
  
  <p>If I wanted to change propertyOne I would (at the moment) do:</p>
  
  <pre><code>this.setState({...this.state, propertyOne: 'new value'})
  </code></pre>
  
  <p>I assumed this was needed to 'remember' the other two values, however, it appears if I do not include <code>...this.state</code> the other two values still remain.</p>
  
  <pre><code>this.setState({propertyOne: 'new value'})
  </code></pre>
  
  <p>So, my question is, do I need <code>...this.state</code>? Why do some people on the internet seem to suggest using it?</p>