build.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.NODE_ENV = 'production';

// 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 chalk = require('chalk');
const fs = require('fs-extra');
const path = require('path');
const url = require('url');
const webpack = require('webpack');
const config = require('../config/webpack.config.prod');
const paths = require('../config/paths');
const checkRequiredFiles = require('react-dev-utils/checkRequiredFiles');
const FileSizeReporter = require('react-dev-utils/FileSizeReporter');

const measureFileSizesBeforeBuild = FileSizeReporter.measureFileSizesBeforeBuild;
const printFileSizesAfterBuild = FileSizeReporter.printFileSizesAfterBuild;
const useYarn = fs.existsSync(paths.yarnLockFile);

// Warn and crash if required files are missing
if (!checkRequiredFiles([paths.appHtml, paths.appIndexJs])) {
  process.exit(1);
}

// First, read the current file sizes in build directory.
// This lets us display how much they changed later.
measureFileSizesBeforeBuild(paths.appBuild).then(previousFileSizes => {
  // Remove all content but keep the directory so that
  // if you're in it, you don't end up in Trash
  fs.emptyDirSync(paths.appBuild);

  // Start the webpack build
  build(previousFileSizes);

  // Merge with the public folder
  copyPublicFolder();
});

// Print out errors
function printErrors(summary, errors) {
  console.log(chalk.red(summary));
  console.log();
  errors.forEach(err => {
    console.log(err.message || err);
    console.log();
  });
}

// Create the production build and print the deployment instructions.
function build(previousFileSizes) {