title: Add an object with setState() to an array of objects
body: <p>My component's state is an array of objects:</p>
  
  <pre><code>this.state = {
    userFavorites: [{id: 1, title: 'A'}, {id: 2, title: 'B'}]
  }
  </code></pre>
  
  <p>I need to, everytime I click in a button, update my state with another object like the ones I have in my state above; for example: {id: 3, title: 'C'}.</p>
  
  <p>If I simply concat them and set the state, the last object keeps being changed by the one that's being added.</p>
  
  <p>Do I need the spread operator here?</p>