create-react-app/packages/react-dev-utils/webpackHotDevClient.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.
 */

'use strict';

// This alternative WebpackDevServer combines the functionality of:
// https://github.com/webpack/webpack-dev-server/blob/webpack-1/client/index.js
// https://github.com/webpack/webpack/blob/webpack-1/hot/dev-server.js

// It only supports their simplest configuration (hot updates on same server).
// It makes some opinionated choices on top, like adding a syntax error overlay
// that looks similar to our console output. The error overlay is inspired by:
// https://github.com/glenjamin/webpack-hot-middleware

var SockJS = require('sockjs-client');
var stripAnsi = require('strip-ansi');
var url = require('url');
var launchEditorEndpoint = require('./launchEditorEndpoint');
var formatWebpackMessages = require('./formatWebpackMessages');
var ErrorOverlay = require('react-error-overlay');

ErrorOverlay.startReportingRuntimeErrors({
  launchEditorEndpoint: launchEditorEndpoint,
  onError: function() {
    // TODO: why do we need this?
    if (module.hot && typeof module.hot.decline === 'function') {
      module.hot.decline();
    }
  },
});

if (module.hot && typeof module.hot.dispose === 'function') {
  module.hot.dispose(function() {
    // TODO: why do we need this?
    ErrorOverlay.stopReportingRuntimeErrors();
  });
}

// Connect to WebpackDevServer via a socket.
var connection = new SockJS(
  url.format({
    protocol: window.location.protocol,
    hostname: window.location.hostname,
    port: window.location.port,
    // Hardcoded in WebpackDevServer
    pathname: '/sockjs-node',
  })
);

// Unlike WebpackDevServer client, we won't try to reconnect
// to avoid spamming the console. Disconnect usually happens
// when developer stops the server.
connection.onclose = function() {
  if (typeof console !== 'undefined' && typeof console.info === 'function') {
    console.info(
      'The development server has disconnected.\nRefresh the page if necessary.'
    );
  }
};

// Remember some state related to hot module replacement.
var isFirstCompilation = true;
var mostRecentCompilationHash = null;
var hasCompileErrors = false;

function clearOutdatedErrors() {
  // Clean up outdated compile errors, if any.
  if (typeof console !== 'undefined' && typeof console.clear === 'function') {
    if (hasCompileErrors) {
      console.clear();
    }
  }
}

// Successful compilation.
function handleSuccess() {
  clearOutdatedErrors();

  var isHotUpdate = !isFirstCompilation;
  isFirstCompilation = false;
  hasCompileErrors = false;

  // Attempt to apply hot updates or reload.
  if (isHotUpdate) {
    tryApplyUpdates(function onHotUpdateSuccess() {
      // Only dismiss it when we're sure it's a hot update.
      // Otherwise it would flicker right before the reload.
      ErrorOverlay.dismissBuildError();
    });
  }
}

// Compilation with warnings (e.g. ESLint).
function handleWarnings(warnings) {
  clearOutdatedErrors();

  var isHotUpdate = !isFirstCompilation;
  isFirstCompilation = false;
  hasCompileErrors = false;

  function printWarnings() {
    // Print warnings to the console.
    var formatted = formatWebpackMessages({
      warnings: warnings,
      errors: [],
    });

    if (typeof console !== 'undefined' && typeof console.warn === 'function') {
      for (var i = 0; i < formatted.warnings.length; i++) {
        if (i === 5) {
          console.warn(
            'There were more warnings in other files.\n' +
              'You can find a complete log in the terminal.'
          );
          break;
        }
        console.warn(stripAnsi(formatted.warnings[i]));
      }
    }
  }

  // Attempt to apply hot updates or reload.
  if (isHotUpdate) {
    tryApplyUpdates(function onSuccessfulHotUpdate() {
      // Only print warnings if we aren't refreshing the page.
      // Otherwise they'll disappear right away anyway.
      printWarnings();
      // Only dismiss it when we're sure it's a hot update.
      // Otherwise it would flicker right before the reload.
      ErrorOverlay.dismissBuildError();
    });
  } else {
    // Print initial warnings immediately.
    printWarnings();
  }
}

// Compilation with errors (e.g. syntax error or missing modules).
function handleErrors(errors) {
  clearOutdatedErrors();

  isFirstCompilation = false;
  hasCompileErrors = true;

  // "Massage" webpack messages.
  var formatted = formatWebpackMessages({
    errors: errors,
    warnings: [],
  });

  // Only show the first error.
  ErrorOverlay.reportBuildError(formatted.errors[0]);

  // Also log them to the console.
  if (typeof console !== 'undefined' && typeof console.error === 'function') {
    for (var i = 0; i < formatted.errors.length; i++) {
      console.error(stripAnsi(formatted.errors[i]));
    }
  }

  // Do not attempt to reload now.
  // We will reload on next success instead.
}

// There is a newer version of the code available.
function handleAvailableHash(hash) {
  // Update last known compilation hash.
  mostRecentCompilationHash = hash;
}

// Handle messages from the server.
connection.onmessage = function(e) {
  var message = JSON.parse(e.data);
  switch (message.type) {
    case 'hash':
      handleAvailableHash(message.data);
      break;
    case 'still-ok':
    case 'ok':
      handleSuccess();
      break;
    case 'content-changed':
      // Triggered when a file from `contentBase` changed.
      window.location.reload();
      break;
    case 'warnings':
      handleWarnings(message.data);
      break;
    case 'errors':
      handleErrors(message.data);
      break;
    default:
    // Do nothing.
  }
};

// Is there a newer version of this code available?
function isUpdateAvailable() {
  /* globals __webpack_hash__ */
  // __webpack_hash__ is the hash of the current compilation.
  // It's a global variable injected by Webpack.
  return mostRecentCompilationHash !== __webpack_hash__;
}

// Webpack disallows updates in other states.
function canApplyUpdates() {
  return module.hot.status() === 'idle';
}

// Attempt to update code on the fly, fall back to a hard reload.
function tryApplyUpdates(onHotUpdateSuccess) {
  if (!module.hot) {
    // HotModuleReplacementPlugin is not in Webpack configuration.
    window.location.reload();
    return;
  }

  if (!isUpdateAvailable() || !canApplyUpdates()) {
    return;
  }

  function handleApplyUpdates(err, updatedModules) {
    if (err || !updatedModules) {
      window.location.reload();
      return;
    }

    if (typeof onHotUpdateSuccess === 'function') {
      // Maybe we want to do something.
      onHotUpdateSuccess();
    }

    if (isUpdateAvailable()) {
      // While we were updating, there was a new update! Do it again.
      tryApplyUpdates();
    }
  }

  // https://webpack.github.io/docs/hot-module-replacement.html#check
  var result = module.hot.check(/* autoApply */ true, handleApplyUpdates);

  // // Webpack 2 returns a Promise instead of invoking a callback
  if (result && result.then) {
    result.then(
      function(updatedModules) {
        handleApplyUpdates(null, updatedModules);
      },
      function(err) {
        handleApplyUpdates(err, null);
      }
    );
  }
}