title: Uncaught TypeError: Cannot assign to read only property 'background' of object '#<Object>'
body: <p>my project is babel7.</p>
  
  <pre><code>render() {
    const {elementStyle, style } = this.props;
    return (
              &lt;span style={Object.assign(elementStyle, style)}&gt;{label} 
              &lt;/span&gt;
          )
  }
  </code></pre>
  
  <p>//Object.assign(elementStyle, style) --> error.
  but i correct Object.assign({}, elementStyle, style)  is working.
  and why is not working?? 
   i debuggered this code. at first is working but when reredering, this code is error...
  i don't know please help me.</p>