customDevClientPort.diff

--- webpackHotDevClient.orig.js	2019-10-24 21:33:25.464549772 +0200
+++ webpackHotDevClient.js	2019-10-24 21:40:27.485125571 +0200
@@ -22,7 +22,7 @@
     url.format({
       protocol: window.location.protocol,
       hostname: window.location.hostname,
-      port: parseInt(process.env.PORT || window.location.port, 10) + 1,
+      port: process.env.RAZZLE_HOTCLIENT_NOPORT ? '' : parseInt(process.env.PORT || window.location.port, 10) + 1,
       pathname: launchEditorEndpoint,
       search:
         '?fileName=' +
@@ -62,7 +62,7 @@
   url.format({
     protocol: window.location.protocol,
     hostname: window.location.hostname,
-    port: parseInt(process.env.PORT || window.location.port, 10) + 1,
+    port: process.env.RAZZLE_HOTCLIENT_NOPORT ? '' : parseInt(process.env.PORT || window.location.port, 10) + 1,
     // Hardcoded in WebpackDevServer
     pathname: '/sockjs-node',
   })

razzle.config.js

'use strict';

module.exports = {
  modify: (defaultConfig, { target, dev }, webpack) => {
    const config = defaultConfig;

    if (dev) {

      if (target === 'web') {
        config.devServer.quiet = false;
        config.devServer.public = 'localhost:443';
      }

      config.module.rules = config.module.rules.reduce((rules, rule) => {
        if (rule.test &&
          rule.test.toString()===/\.(js|jsx|mjs)$/.toString() &&
          !rule.enforce) {

          const { use, ...rest } = rule;

          rules.push({ ...rule, ...{
            exclude: /razzle-dev-utils\/webpackHotDevClient\.js/
          }});
          
          // yarn add patch-loader
          // Use env var RAZZLE_HOTCLIENT_NOPORT=true
          rules.push({ ...rest, ...{ 
            use: [ ...use, {
              loader: require.resolve('patch-loader'),
              options: { patch: '../../customDevClientPort.diff' },
            }],
            include: /razzle-dev-utils\/webpackHotDevClient\.js/,
          }});

        }
        else {
          rules.push(rule);
        } 
        return rules;
      }, []);
    }
    return config;
  }
};