title: Remove value from object without mutation
body: <p>What's a good and short way to remove a value from an object at a specific key without mutating the original object?</p>
  
  <p>I'd like to do something like:</p>
  
  <pre><code>let o = {firstname: 'Jane', lastname: 'Doe'};
  let o2 = doSomething(o, 'lastname');
  console.log(o.lastname); // 'Doe'
  console.log(o2.lastname); // undefined
  </code></pre>
  
  <p>I know there are a lot of immutability libraries for such tasks, but I'd like to get away without a library. But to do this, a requirement would be to have an easy and short way that can be used throughout the code, without abstracting the method away as a utility function.</p>
  
  <p>E.g. for adding a value I do the following:</p>
  
  <p><code>let o2 = {...o1, age: 31};</code></p>
  
  <p>This is quite short, easy to remember and doesn't need a utility function.</p>
  
  <p>Is there something like this for removing a value? ES6 is very welcome.</p>
  
  <p>Thank you very much!</p>