title: React add property to immutable object
body: <p>I'm trying to add a new property to objects within an array. My idea was to do something like this: </p>
  
  <pre><code>class Foo extends Component {
      constructor(props) {
          super(props);
  
          this.state = this.getInitialState();
          console.log(this.state); //Property "label" is missing in "members" array
      }
  
      /**
       * Get initial state
       * @returns {{title, description}}
       */
      getInitialState = () =&gt; {
          let members = this.props.members.slice();
          members.map((member) =&gt; {
              return {
                  ...member,
                  label: (member.firstName + " " + member.lastName)
              }
          });
          console.log(members); //"label" is not a property of objects
  
          return {title: "", description: "", responsible: [], typeOf: null, 
                  members: members};
      };
  
      render () {
           return (&lt;div/&gt;)
      }
  }
  </code></pre>
  
  <p>I want <code>members</code> to stay/remain immutable, yet adding another property to every object within this array. What am I doing wrong here? Thanks!</p>