Why doesn't webpack-dev-server rebuild the project?

Question

JavaScript

This is the webpack config

var path = require('path')

const dev = process.env.NODE_ENV !== "production"

module.exports = {
    mode: dev ? "development" : "production",
    entry: './src/index.js',
    output: {
        path: path.resolve(__dirname, 'public/dist'),
        filename: 'bundle.js',
        publicPath: 'dist/'
    },
    devServer: {
        overlay: true,
        contentBase: path.join(__dirname, '/public'),
        historyApiFallback: true,
        port: 3333,
    },
    module: {
        rules: [
            {
                test: /\.js$/,
                use: [
                    { loader: "babel-loader" }
                  ]
            },
            {
                test: /\.css$/,
                use: [
                  { loader: "style-loader" },
                  { loader: "css-loader" }
                ]
            }
        ]
    }
}

this is an excerpt from package.json

"scripts": {
    "dev": "webpack-dev-server",
    "start": "npm run dev"
  },

The first time at startup it builds normally. But then when you update the code, it will not change until you run npm start again