React-router v4 - cannot GET *url*

It worked for me just need just addding devServer { historyApiFallback: true } is OK, not need use publicPath: '/'

usage like:

  devServer: {
    historyApiFallback: true
  },

Just to supplement Tyler's answer for anyone still struggling with this:

Adding the devServer.historyApiFallback: true to my webpack config (without setting publicPath) fixed the 404/Cannot-GET errors I was seeing on refresh/back/forward, but only for a single level of nested route. In other words, "/" and "/topics" started working fine but anything beyond that (e.g. "/topics/whatever") still threw a 404 on refresh/etc.

Just came across the accepted answer here: Unexpected token < error in react router component and it provided the last missing piece for me. Adding the leading / to the bundle script src in my index.html has solved the issue completely.

I'm assuming you're using Webpack. If so, adding a few things to your webpack config should solve the issue. Specifically, output.publicPath = '/' and devServer.historyApiFallback = true. Here's an example webpack config below which uses both of ^ and fixes the refresh issue for me. If you're curious "why", this will help.

var path = require('path');
var HtmlWebpackPlugin = require('html-webpack-plugin');

module.exports = {
  entry: './app/index.js',
  output: {
    path: path.resolve(__dirname, 'dist'),
    filename: 'index_bundle.js',
    publicPath: '/'
  },
  module: {
    rules: [
      { test: /\.(js)$/, use: 'babel-loader' },
      { test: /\.css$/, use: [ 'style-loader', 'css-loader' ]}
    ]
  },
  devServer: {
    historyApiFallback: true,
  },
  plugins: [
    new HtmlWebpackPlugin({
      template: 'app/index.html'
    })
  ]
};

I wrote more about this here - Fixing the "cannot GET /URL" error on refresh with React Router (or how client side routers work)

If your application is hosted on a static file server, you need to use a instead of a .

import { HashRouter } from 'react-router-dom'

ReactDOM.render((
  <HashRouter>
    <App />
  </HashRouter>
), holder)

https://github.com/ReactTraining/react-router/blob/v4.1.1/FAQ.md#why-doesnt-my-application-render-after-refreshing