title: How are UMD and CommonJS (CJS) package folders different, and which should I use?
body: <p>I installed reactjs and react-dom like this with package.json</p>
  <pre class="lang-json prettyprint-override"><code>    &quot;dependencies&quot;: {
          &quot;bootstrap&quot;: &quot;^v4.1.1&quot;,
          &quot;popper.js&quot;: &quot;^1.14.3&quot;,
          &quot;react&quot;: &quot;^v16.4.1&quot;,
          &quot;react-dom&quot;: &quot;^16.4.1&quot;
      }
  </code></pre>
  <p>It downloaded <code>react</code> folder and <code>react-dom</code> folder correctly.</p>
  <p>Both folders have <code>cjs</code> and <code>umd</code> folder and they have a lot of JavaScript files.</p>
  <p>For me it's unable to find difference between files in two folders.</p>
  <p>Like this:</p>
  <pre class="lang-none prettyprint-override"><code>    URL: node_modules/react/umd
        react-development.js
        react-production.min.js
  
      URL: node_modules/react/cjs
         react-development.js
         react-production.min.js
  </code></pre>
  <p>almost same with react-dom. It also has <code>cjs</code> and <code>umd</code> folder and I don't know which file from which folder should I use to develop a React application or website.</p>