title: Call a function after leaving input field
body: <p>On a contact form, I have several input fields. One of those fields, is an email address field:</p>
  
  <pre><code>&lt;input type='text' name='input_email' onChange={this.validateEmail}/&gt;
  </code></pre>
  
  <p>Right now, I have the email validation function set to the onChange attribute. Thus, while the user is entering characters into the email field, an error message appears the whole time.</p>
  
  <p>I want to change this, so that <code>this.validateEmail</code> only gets called once when the user leaves that specific input field. How would I accomplish this? </p>
  
  <p>I can't find any default object events that would solve this issue.</p>
  
  <p>FYI, using ReactJS</p>