create-react-app/scripts/start.js

/**
 * 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.
 */

process.env.NODE_ENV = 'development';

var path = require('path');
var chalk = require('chalk');
var webpack = require('webpack');
var WebpackDevServer = require('webpack-dev-server');
var execSync = require('child_process').execSync;
var opn = require('opn');
var detect = require('detect-port');
var prompt = require('./utils/prompt');
var config = require('../config/webpack.config.dev');

// Tools like Cloud9 rely on this.
var DEFAULT_PORT = process.env.PORT || 3000;
var compiler;

// TODO: hide this behind a flag and eliminate dead code on eject.
// This shouldn't be exposed to the user.
var handleCompile;
var isSmokeTest = process.argv.some(arg => arg.indexOf('--smoke-test') > -1);
if (isSmokeTest) {
  handleCompile = function (err, stats) {
    if (err || stats.hasErrors() || stats.hasWarnings()) {
      process.exit(1);
    } else {
      process.exit(0);
    }
  };
}

// Some custom utilities to prettify Webpack output.
// This is a little hacky.
// It would be easier if webpack provided a rich error object.
var friendlySyntaxErrorLabel = 'Syntax error:';
function isLikelyASyntaxError(message) {
  return message.indexOf(friendlySyntaxErrorLabel) !== -1;
}
function formatMessage(message) {
  return message
    // Make some common errors shorter:
    .replace(
      // Babel syntax error
      'Module build failed: SyntaxError:',
      friendlySyntaxErrorLabel
    )
    .replace(
      // Webpack file not found error
      /Module not found: Error: Cannot resolve 'file' or 'directory'/,
      'Module not found:'
    )
    // Internal stacks are generally useless so we strip them
    .replace(/^\s*at\s.*:\d+:\d+[\s\)]*\n/gm, '') // at ... ...:x:y
    // Webpack loader names obscure CSS filenames
    .replace('./~/css-loader!./~/postcss-loader!', '');
}

function clearConsole() {
  // This seems to work best on Windows and other systems.
  // The intention is to clear the output so you can focus on most recent build.
  process.stdout.write('\x1bc');
}

function setupCompiler(port) {
  // "Compiler" is a low-level interface to Webpack.
  // It lets us listen to some events and provide our own custom messages.
  compiler = webpack(config, handleCompile);

  // "invalid" event fires when you have changed a file, and Webpack is
  // recompiling a bundle. WebpackDevServer takes care to pause serving the
  // bundle, so if you refresh, it'll wait instead of serving the old one.
  // "invalid" is short for "bundle invalidated", it doesn't imply any errors.
  compiler.plugin('invalid', function() {
    clearConsole();
    console.log('Compiling...');
  });

  // "done" event fires when Webpack has finished recompiling the bundle.
  // Whether or not you have warnings or errors, you will get this event.
  compiler.plugin('done', function(stats) {
    clearConsole();
    var hasErrors = stats.hasErrors();
    var hasWarnings = stats.hasWarnings();
    if (!hasErrors && !hasWarnings) {
      console.log(chalk.green('Compiled successfully!'));
      console.log();
      console.log('The app is running at:');
      console.log();
      console.log('  ' + chalk.cyan('http://localhost:' + port + '/'));
      console.log();
      console.log('Note that the development build is not optimized.');
      console.log('To create a production build, use ' + chalk.cyan('npm run build') + '.');
      console.log();
      return;
    }

    // We have switched off the default Webpack output in WebpackDevServer
    // options so we are going to "massage" the warnings and errors and present
    // them in a readable focused way.
    var json = stats.toJson();
    var formattedErrors = json.errors.map(message =>
      'Error in ' + formatMessage(message)
    );
    var formattedWarnings = json.warnings.map(message =>
      'Warning in ' + formatMessage(message)
    );
    if (hasErrors) {
      console.log(chalk.red('Failed to compile.'));
      console.log();
      if (formattedErrors.some(isLikelyASyntaxError)) {
        // If there are any syntax errors, show just them.
        // This prevents a confusing ESLint parsing error
        // preceding a much more useful Babel syntax error.
        formattedErrors = formattedErrors.filter(isLikelyASyntaxError);
      }
      formattedErrors.forEach(message => {
        console.log(message);
        console.log();
      });
      // If errors exist, ignore warnings.
      return;
    }
    if (hasWarnings) {
      console.log(chalk.yellow('Compiled with warnings.'));
      console.log();
      formattedWarnings.forEach(message => {
        console.log(message);
        console.log();
      });
      // Teach some ESLint tricks.
      console.log('You may use special comments to disable some warnings.');
      console.log('Use ' + chalk.yellow('// eslint-disable-next-line') + ' to ignore the next line.');
      console.log('Use ' + chalk.yellow('/* eslint-disable */') + ' to ignore all warnings in a file.');
    }
  });
}

function openBrowser(port) {
  if (process.platform === 'darwin') {
    try {
      // Try our best to reuse existing tab
      // on OS X Google Chrome with AppleScript
      execSync('ps cax | grep "Google Chrome"');
      execSync(
        'osascript chrome.applescript http://localhost:' + port + '/',
        {cwd: path.join(__dirname, 'utils'), stdio: 'ignore'}
      );
      return;
    } catch (err) {
      // Ignore errors.
    }
  }
  // Fallback to opn
  // (It will always open new tab)
  opn('http://localhost:' + port + '/');
}

function runDevServer(port) {
  // Launch WebpackDevServer.
  new WebpackDevServer(compiler, {
    // When an unrecognized URL is requested (e.g. localhost:3000/todos),
    // assume that this is a single-page app, and serve index.html.
    historyApiFallback: true,
    // Enable hot reloading server. It will provide /sockjs-node/ endpoint
    // for the WebpackDevServer client so it can learn when the files were
    // updated. The WebpackDevServer client is included as an entry point
    // in the Webpack development configuration. Note that only changes
    // to CSS are currently hot reloaded. JS changes will refresh the browser.
    hot: true,
    // It is important to tell WebpackDevServer to use the same "root" path
    // as we specified in the config. In development, we always serve from /.
    publicPath: config.output.publicPath,
    // WebpackDevServer is noisy by default so we emit custom message instead
    // by listening to the compiler events with `compiler.plugin` calls above.
    quiet: true,
    // Reportedly, this avoids CPU overload on some systems.
    // https://github.com/facebookincubator/create-react-app/issues/293
    watchOptions: {
      ignored: /node_modules/
    }
  }).listen(port, (err, result) => {
    if (err) {
      return console.log(err);
    }

    clearConsole();
    console.log(chalk.cyan('Starting the development server...'));
    console.log();
    openBrowser(port);
  });
}

function run(port) {
  setupCompiler(port);
  runDevServer(port);
}

// 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.
detect(DEFAULT_PORT).then(port => {
  if (port === DEFAULT_PORT) {
    run(port);
    return;
  }

  clearConsole();
  var question =
    chalk.yellow('Something is already running on port ' + DEFAULT_PORT + '.') +
    '\n\nWould you like to run the app on another port instead?';

  prompt(question, true).then(shouldChangePort => {
    if (shouldChangePort) {
      run(port);
    }
  });
});