title: How to fix error 'FB' is not defined no-undef on create-react-app project?
body: <p>I made the project using this link as my starting file.</p>
  
  <p><a href="https://github.com/facebookincubator/create-react-app" rel="noreferrer">https://github.com/facebookincubator/create-react-app</a></p>
  
  <p>But after i tried to make Facebook login button with follow by their official docs with this.</p>
  
  <pre><code>componentDidMount(){
      console.log('login mount');
      window.fbAsyncInit = function() {
          FB.init({
              appId      : '320866754951228',
              xfbml      : true,
              version    : 'v2.6'
          });
  
          FB.getLoginStatus(function(response) {
              //this.statusChangeCallback(response);
          });
  
      };
  
      (function(d, s, id){
          var js, fjs = d.getElementsByTagName(s)[0];
          if (d.getElementById(id)) {return;}
          js = d.createElement(s); js.id = id;
          js.src = "//connect.facebook.net/en_US/sdk.js";
          fjs.parentNode.insertBefore(js, fjs);
      }(document, 'script', 'facebook-jssdk'));
  }
  </code></pre>
  
  <p>So i got this errors when the browser was refreshed.</p>
  
  <pre><code>Failed to compile.
  
  Error in ./src/components/user_profile/LoginForm.js
  
  /Sites/full_stack_production/xxxxx
    70:13  error  'FB' is not defined  no-undef
    76:13  error  'FB' is not defined  no-undef
  
  ✖ 2 problems (2 errors, 0 warnings)
  </code></pre>
  
  <p>So i guess because ESLint that cause this errors.
  How can i fix this or make the exception for this <code>FB</code> variable?</p>
  
  <p>Thanks! </p>