title: Can I use NODE_ENV="staging" with mode="production" in webpack 4?
body: <p>My app use NODE_ENV for deciding which api server should request to.</p>
  
  <pre><code>NODE_ENV="production" =&gt; https://api.***/
  NODE_ENV="staging" =&gt; https://api.staging-***/
  NODE_ENV="development" =&gt; http://localhost:3000/
  </code></pre>
  
  <p>I want to build staging bundle with mode="production" but keep NODE_ENV="staging".</p>
  
  <p>I try to build with config below, but bundle.js becomes NODE_ENV="production".</p>
  
  <pre><code>{
     mode: "production",
     plugins: [
       new webpack.DefinePlugin({
         'process.env': {
           'NODE_ENV': JSON.stringify("staging")
         }
       })
     ]
   }
  </code></pre>