text: 'use strict';
  
  // Do this as the first thing so that any code reading it knows the right env.
  process.env.BABEL_ENV = 'development';
  process.env.NODE_ENV = 'development';
  
  // Makes the script crash on unhandled rejections instead of silently
  // ignoring them. In the future, promise rejections that are not handled will
  // terminate the Node.js process with a non-zero exit code.
  process.on('unhandledRejection', err => {
    throw err;
  });
  
  // Ensure environment variables are read.
  require('../config/env');
  
  const fs = require('fs');
  const chalk = require('chalk');
  const webpack = require('webpack');
  const WebpackDevServer = require('webpack-dev-server');
  const clearConsole = require('react-dev-utils/clearConsole');
  const checkRequiredFiles = require('react-dev-utils/checkRequiredFiles');
  const {
    choosePort,
    createCompiler,
    prepareProxy,
    prepareUrls,
  } = require('react-dev-utils/WebpackDevServerUtils');
  const openBrowser = require('react-dev-utils/openBrowser');
  const paths = require('../config/paths');
  const config = require('../config/webpack.config.dev');
  const createDevServerConfig = require('../config/webpackDevServer.config');
  
  const useYarn = fs.existsSync(paths.yarnLockFile);
  const isInteractive = process.stdout.isTTY;
  
  // Warn and crash if required files are missing
  if (!checkRequiredFiles([paths.appHtml, paths.appIndexJs])) {
    process.exit(1);
  }
  
  // Tools like Cloud9 rely on this.
  const DEFAULT_PORT = parseInt(process.env.PORT, 10) || 8080;
  const HOST = process.env.HOST || '0.0.0.0';
  
  if (process.env.HOST) {
    console.log(
      chalk.cyan(
        `Attempting to bind to HOST environment variable: ${chalk.yellow(
          chalk.bold(process.env.HOST)
        )}`
      )
    );
    console.log(
      `If this was unintentional, check that you haven't mistakenly set it in your shell.`
    );
    console.log(`Learn more here: ${chalk.yellow('http://bit.ly/2mwWSwH')}`);
    console.log();
  }
  
  // We attempt to use the default port but if it is busy, we offer the user to
  // run on a different port. `choosePort()` Promise resolves to the next free port.
  choosePort(HOST, DEFAULT_PORT)
    .then(port => {
      if (port == null) {
        // We have not found a port.
        return;
      }
      const protocol = process.env.HTTPS === 'true' ? 'https' : 'http';
      const appName = require(paths.appPackageJson).name;
      const urls = prepareUrls(protocol, HOST, port);
      // Create a webpack compiler that is configured with custom messages.
      const compiler = createCompiler(webpack, config, appName, urls, useYarn);
      // Load proxy config
      const proxySetting = require(paths.appPackageJson).proxy;
      const proxyConfig = prepareProxy(proxySetting, paths.appPublic);
      // Serve webpack assets generated by the compiler over a web sever.
      const serverConfig = createDevServerConfig(
        proxyConfig,
        urls.lanUrlForConfig
      );
      const devServer = new WebpackDevServer(compiler, serverConfig);
      // Launch WebpackDevServer.
      devServer.listen(port, HOST, err => {
        if (err) {
          return console.log(err);
        }
        if (isInteractive) {
          clearConsole();
        }
        console.log(chalk.cyan('Starting the development server...\n'));
        openBrowser(urls.localUrlForBrowser);
      });
  
      ['SIGINT', 'SIGTERM'].forEach(function(sig) {
        process.on(sig, function() {
          devServer.close();
          process.exit();
        });
      });
    })
    .catch(err => {
      if (err && err.message) {
        console.log(err.message);
      }
      process.exit(1);
    });
  