title: React component not rerender on state change
body: <p>I'm rendering the following form component <strong>twice</strong> in an other component. Problem is that when I enter a value in one of the rendered forms, it doesn't update the placeholder of the other form. How do I get react to re-render component after state change so that both forms have the same placeholder value?</p>
  
  <p>Here's a fiddle: <a href="https://jsfiddle.net/o4h5af4g/7/" rel="nofollow noreferrer">https://jsfiddle.net/o4h5af4g/7/</a></p>
  
  <pre><code>import React, { Component } from 'react';
  
  class LengthForm extends Component {
    constructor(props){
      super(props)
      this.state = {
        length:1
      };
    }
  
   handleChange(event) {
     this.setState({length: event.target.value});
   }
  
   render() {
      return (
        &lt;div className="LenghtForm"&gt;
          &lt;input name="length" onChange={this.handleChange.bind(this)} type="integer" placeholder={this.state.length}/&gt;
        &lt;/div&gt;
      );
    }
  }
  
  export default LengthForm;
  </code></pre>