title: Enable CORS in my React App with Node.js backend
body: <p>I used create-react-app to build my react app. This app does a POST call on another API (elasticsearch), hosted on a different server (not owned/managed by me). So once the user enters the data in the form, onSubmit basically calls getResponse() method that makes the call. 
  Initialize client:</p>
  
  <pre><code>let client = new elasticsearch.Client({
      host: "https://{cred.user}:{cred.pass}@@servername.domain:11121",
      log: "trace",
  });
  </code></pre>
  
  <p>API query:</p>
  
  <pre><code>getResponse = () =&gt; {
          client
            .search({
              index: 'custom_index_1',
              body: {
                  query: {
                      match: {"data": this.state.data}
                  },
              }
          },function(error, response, status) {
              if (error) {
                  const errorMessage= {error};
                  console.log(errorMessage);
              }
              else {
                  this.setState({results: response.hits.hits});
                  console.log(this.state.results);
              }
          });
      }
  </code></pre>
  
  <p>But I'm getting the CORS error as follows:</p>
  
  <pre><code>Failed to load resource: the server responded with a status of 403 (Forbidden)
  localhost/:1 Access to XMLHttpRequest at 'https://servername.domain:11121/' from origin 'http://localhost:3000' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.console.js:40 
  WARNING: 2019-11-21T07:54:32Z No living connections
  </code></pre>
  
  <p>After reading in SO about the same issue, I found that using the cors npm module can fix this issue (at least in development). But I do not understand where do I put this code:</p>
  
  <pre><code>var express = require('express')
  var cors = require('cors')
  var app = express()
  app.use(cors())
  </code></pre>
  
  <p>OR</p>
  
  <pre><code>var express = require('express')
  var cors = require('cors')
  var app = express()
  
  app.use(cors())
  
  app.get('/products/:id', function (req, res, next) {
    res.json({msg: 'This is CORS-enabled for all origins!'})
  })
  
  app.listen(80, function () {
    console.log('CORS-enabled web server listening on port 80')
  })
  </code></pre>
  
  <p>My questions are as follows:
  1. Where do I add this code above? in my react app's app.js? If yes, can someone give me an example please. I am using something like this:</p>
  
  <pre><code>import statements
  class App extends Component {
   &lt;code&gt;
  }
  export default App;
  </code></pre>
  
  <ol start="2">
  <li><p>If this code is to be added to some other file then which file? Is it server.js? If yes, where do I find this? I'm using Windows 7. Node is installed in a customer directory: C:\MYSW\NodeJs\12.1.0. I see some server.js in here: C:\Users\user1\Scratch\node\myreact_ui\node_modules\react-dom\server.js, but is it the right file</p></li>
  <li><p>Please give me a sample of how the code is added and where exactly in the file. I am new to React and Node so I do not know much about the internals. I'v been stuck here for days now and really need some help. Thanks.</p></li>
  </ol>
  
  <p>Everywhere it says, add this code and it work, no one mentions where do I add it and how? Any help appreciated.</p>