title: Typescript Filter and return single key
body: <p>I have a set of checkboxes that allow a user to check which roles to assign to a new user.  I am able to filter back and get only the checkboxes that are actually checked, however, I am having trouble finding the best way to just return the "name" key of those checked checkboxes.  </p>
  
  <pre><code>userToAdd.roles = this.roles.filter( (role) =&gt; role.checked );
  </code></pre>
  
  <p>Is there a way to use a reduce, or basically just say "role.name" in the filter so I don't return the entire object?  I can do this with a for loop, but I'm curious if there is a better way to just return the name key as part of the filter?</p>
  
  <p>This is how the object looks now, which is wrong:</p>
  
  <pre><code>{
    "firstName": "sfsdfds",
    "username": "fdsfsdf",
    "lastName": "sdfsdfsdf",
    "email": "dsfsdfdsf",
    "roles": [
      {
        "ID": "ce97fb46-7e04-4a4f-b393-5a5492b558fb",
        "name": "admin",
        "checked": true
      },
      {
        "ID": "e89bacd2-4140-46a1-9a2b-0f85aa9f9ca0",
        "name": "offline_access",
        "checked": true
      }
    ],
    "password": "pass"
  }
  </code></pre>
  
  <p>This is how the object should look, in the roles array i just include the name, not the ID or checked keys:</p>
  
  <pre><code>{
    "firstName": "testing",
    "lastName": "testing",
    "username": "testing",
    "email": "testing",
    "roles": [
      "uma_authorization",
      "offline_access"
    ],
    "password": "pass"
  }
  </code></pre>