Actually, I think the real reason is that useSubscription creates a useEffect that calls subscribe that gets called every time the component gets rerendered. I think the intent is that subscribe is a useCallback, so it should be memoized, but that doesn't actually prevent subsequent calls to subscribe: it just memoizes the passing of the particular topic and options parameters.

Hey @Aposhian thanks again for the contribution, I was doing some testing on the alpha version and there is a big problem with webpack 5 and react too. what configuration are you using now? I think we can use precompiled-mqtt for temporary solution, what you think? I'll do some tests with you new createSubscription

I have been getting it to work with Webpack 5 by replacing Create React App with react-app-rewired, and then using the following Webpack overrides:

const webpack = require('webpack');
const path = require('path')

module.exports = function override(config) {
  const fallback = config.resolve.fallback || {};
  Object.assign(fallback, {
    "crypto": require.resolve("crypto-browserify"),
    "stream": require.resolve("stream-browserify"),
    "assert": require.resolve("assert"),
    "http": require.resolve("stream-http"),
    "https": require.resolve("https-browserify"),
    "os": require.resolve("os-browserify"),
    "url": require.resolve("url")
  })
  config.resolve.fallback = fallback;
  config.plugins = (config.plugins || []).concat([
    new webpack.ProvidePlugin({
      process: 'process/browser',
      Buffer: ['buffer', 'Buffer']
    })
  ])
  config.module.rules = (config.module.rules || []).concat([
    {
      test: /\.m?js/,
      resolve: {
        fullySpecified: false
      }
    }
  ])
  return config;
}

Hey @Aposhian thanks again for the contribution, I was doing some testing on the alpha version and there is a big problem with webpack 5 and react too. what configuration are you using now? I think we can use precompiled-mqtt for temporary solution, what you think? I'll do some tests with you new createSubscription

Paho-MQTT seems to not have issues, but it would require switching libraries.

Paho MQTT (for JavaScript) appears to not be actively maintained though: it hasn't had a commit in 3 years.

Also, MQTT.js can be made to work just fine with Webpack 5: it just involves readding the polyfills that were removed by default.