start.js

// @remove-on-eject-begin
/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 */
// @remove-on-eject-end
'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 compose = require('promise-compose');
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 webpackAutoDllCompiler = require('react-dev-utils/webpackAutoDllCompiler');
const paths = require('../config/paths');
const config = require('../config/webpack.config.dev');
const dllConfig = require('../config/webpack.config.dll');
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);
}

const configComposer = compose(
  webpackAutoDllCompiler({
    dllConfig,
    paths,
  })
);

configComposer(config).then(config => {
  // Tools like Cloud9 rely on this.
  const DEFAULT_PORT = parseInt(process.env.PORT, 10) || 3000;
  const HOST = process.env.HOST || '0.0.0.0';

  // We attempt to use the default port but if it is busy, we offer the user to
  // run on a different port. `detect()` 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);
    });
});