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

// Do this as the first thing so that any code reading it knows the right env.
process.env.NODE_ENV = 'production';

// Load environment variables from .env file. Suppress warnings using silent
// if this file is missing. dotenv will never modify any environment variables
// that have already been set.
// https://github.com/motdotla/dotenv
require('dotenv').config({silent: true});

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

var 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) {
  console.log('Creating an optimized production build...');

  var compiler;
  try {
    compiler = webpack(config);
  } catch (err) {
    printErrors('Failed to compile.', [err]);
    process.exit(1);
  }

  compiler.run((err, stats) => {
    if (err) {
      printErrors('Failed to compile.', [err]);
      process.exit(1);
    }

    if (stats.compilation.errors.length) {
      printErrors('Failed to compile.', stats.compilation.errors);
      process.exit(1);
    }

    if (process.env.CI && stats.compilation.warnings.length) {
     printErrors('Failed to compile. When process.env.CI = true, warnings are treated as failures. Most CI servers set this automatically.', stats.compilation.warnings);
     process.exit(1);
   }

    console.log(chalk.green('Compiled successfully.'));
    console.log();

    console.log('File sizes after gzip:');
    console.log();
    printFileSizesAfterBuild(stats, previousFileSizes);
    console.log();

    var openCommand = process.platform === 'win32' ? 'start' : 'open';
    var appPackage  = require(paths.appPackageJson);
    var publicUrl = paths.publicUrl;
    var publicPath = config.output.publicPath;
    var publicPathname = url.parse(publicPath).pathname;
    if (publicUrl && publicUrl.indexOf('.github.io/') !== -1) {
      // "homepage": "http://user.github.io/project"
      console.log('The project was built assuming it is hosted at ' + chalk.green(publicPathname) + '.');
      console.log('You can control this with the ' + chalk.green('homepage') + ' field in your '  + chalk.cyan('package.json') + '.');
      console.log();
      console.log('The ' + chalk.cyan('build') + ' folder is ready to be deployed.');
      console.log('To publish it at ' + chalk.green(publicUrl) + ', run:');
      // If script deploy has been added to package.json, skip the instructions
      if (typeof appPackage.scripts.deploy === 'undefined') {
        console.log();
        if (useYarn) {
          console.log('  ' + chalk.cyan('yarn') +  ' add --dev gh-pages');
        } else {
          console.log('  ' + chalk.cyan('npm') +  ' install --save-dev gh-pages');
        }
        console.log();
        console.log('Add the following script in your ' + chalk.cyan('package.json') + '.');
        console.log();
        console.log('    ' + chalk.dim('// ...'));
        console.log('    ' + chalk.yellow('"scripts"') + ': {');
        console.log('      ' + chalk.dim('// ...'));
        console.log('      ' + chalk.yellow('"predeploy"') + ': ' + chalk.yellow('"npm run build",'));
        console.log('      ' + chalk.yellow('"deploy"') + ': ' + chalk.yellow('"gh-pages -d build"'));
        console.log('    }');
        console.log();
        console.log('Then run:');
      }
      console.log();
      console.log('  ' + chalk.cyan(useYarn ? 'yarn' : 'npm') +  ' run deploy');
      console.log();
    } else if (publicPath !== '/') {
      // "homepage": "http://mywebsite.com/project"
      console.log('The project was built assuming it is hosted at ' + chalk.green(publicPath) + '.');
      console.log('You can control this with the ' + chalk.green('homepage') + ' field in your '  + chalk.cyan('package.json') + '.');
      console.log();
      console.log('The ' + chalk.cyan('build') + ' folder is ready to be deployed.');
      console.log();
    } else {
      if (publicUrl) {
        // "homepage": "http://mywebsite.com"
        console.log('The project was built assuming it is hosted at ' + chalk.green(publicUrl) +  '.');
        console.log('You can control this with the ' + chalk.green('homepage') + ' field in your '  + chalk.cyan('package.json') + '.');
        console.log();
      } else {
        // no homepage
        console.log('The project was built assuming it is hosted at the server root.');
        console.log('To override this, specify the ' + chalk.green('homepage') + ' in your '  + chalk.cyan('package.json') + '.');
        console.log('For example, add this to build it for GitHub Pages:')
        console.log();
        console.log('  ' + chalk.green('"homepage"') + chalk.cyan(': ') + chalk.green('"http://myname.github.io/myapp"') + chalk.cyan(','));
        console.log();
      }
      var build = path.relative(process.cwd(), paths.appBuild);
      console.log('The ' + chalk.cyan(build) + ' folder is ready to be deployed.');
      console.log('You may also serve it locally with a static server:')
      console.log();
      if (useYarn) {
        console.log('  ' + chalk.cyan('yarn') +  ' global add pushstate-server');
      } else {
        console.log('  ' + chalk.cyan('npm') +  ' install -g pushstate-server');
      }
      console.log('  ' + chalk.cyan('pushstate-server') + ' ' + build);
      console.log('  ' + chalk.cyan(openCommand) + ' http://localhost:' + (process.env.PORT || 9000));
      console.log();
    }
  });
}

function copyPublicFolder() {
  fs.copySync(paths.appPublic, paths.appBuild, {
    dereference: true,
    filter: file => file !== paths.appHtml
  });
}