title: Better/faster way for changing React array state than cloning it?
body: <p>Whenever a React class has a state object that is or contains an array, updating that state feels awkward. Usually what I do is</p>
  
  <pre><code>var newArrayThing = _.clone(this.state.arrayThing); //or slice()
  newArrayThing[123] = 42; //update stuff
  this.setState({arrayThing: newArrayThing});
  </code></pre>
  
  <p>Is there a better or more elegant way of handling this I am missing? Especially since I always feel this is unnecessary slow if the array is big and the change is small. All that copying for a simple change. But the state should not be edited directly seems to be the mantra.</p>
  
  <p>The Facebook docs mention the Immutability Helpers, but they seem even more far fetched than this.</p>