what is the preferred way to mutate a React state?

Let's say I have a list of plain objects in my this.state.list that I can then use to render a list of children. What then is the right way to insert object into this.state.list?

Below is the only way I think it will work because you can not mutate the this.state directly as mentioned in the doc.

this._list.push(newObject):
this.setState({list: this._list});

This seems ugly to me. Is there a better way?

concat returns a new array, so you can do

this.setState({list: this.state.list.concat([newObject])});

another alternative is React's immutability helper

  var newState = React.addons.update(this.state, {
      list : {
        $push : [newObject]
      }
  });
  
  this.setState(newState);

[setState()][1] can be called with a function as a parameter:

this.setState((state) => ({ list: state.list.concat(newObj) }))

or in ES5:

this.setState(function(state) {
  return {
   list: state.list.concat(newObj)
  }
})

[1]: http://devdocs.io/react/docs/component-api#setstate "setState"

Update 2016

With ES6 you can use:

this.setState({ list: [...this.state.list, ...newObject] });

From the react docs (https://facebook.github.io/react/docs/state-and-lifecycle.html#state-updates-may-be-asynchronous):

> Because this.props and this.state may be updated asynchronously, you should not rely on their values for calculating the next state.

So you should do this instead:

this.setState((prevState) => ({
  contacts: prevState.contacts.concat([contact])
}));