flutter/packages/flutter_tools/lib/src/web/bootstrap.dart

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:meta/meta.dart';

// This logic is taken directly from https://github.com/dart-lang/build/blob/master/build_web_compilers/lib/src/dev_compiler_bootstrap.dart#L272
// It should be fairly stable, but is otherwise required to interact with the client.js script
// vendored with DWDS.
const String _currentDirectoryScript = r'''
var _currentDirectory = (function () {
  var _url;
  var lines = new Error().stack.split('\n');
  function lookupUrl() {
    if (lines.length > 2) {
      var match = lines[1].match(/^\s+at (.+):\d+:\d+$/);
      // Chrome.
      if (match) return match[1];
      // Chrome nested eval case.
      match = lines[1].match(/^\s+at eval [(](.+):\d+:\d+[)]$/);
      if (match) return match[1];
      // Edge.
      match = lines[1].match(/^\s+at.+\((.+):\d+:\d+\)$/);
      if (match) return match[1];
      // Firefox.
      match = lines[0].match(/[<][@](.+):\d+:\d+$/)
      if (match) return match[1];
    }
    // Safari.
    return lines[0].match(/(.+):\d+:\d+$/)[1];
  }
  _url = lookupUrl();
  var lastSlash = _url.lastIndexOf('/');
  if (lastSlash == -1) return _url;
  var currentDirectory = _url.substring(0, lastSlash + 1);
  return currentDirectory;
})();
''';

/// The JavaScript bootstrap script to support in-browser hot restart.
///
/// The [requireUrl] loads our cached RequireJS script file. The [mapperUrl]
/// loads the special Dart stack trace mapper. The [entrypoint] is the
/// actual main.dart file.
///
/// This file is served when the browser requests "main.dart.js" in debug mode,
/// and is responsible for bootstrapping the RequireJS modules and attaching
/// the hot reload hooks.
String generateBootstrapScript({
  @required String requireUrl,
  @required String mapperUrl,
  @required String entrypoint,
}) {
  return '''
"use strict";

// Attach source mapping.
var mapperEl = document.createElement("script");
mapperEl.defer = true;
mapperEl.async = false;
mapperEl.src = "$mapperUrl";
document.head.appendChild(mapperEl);

// Attach require JS.
var requireEl = document.createElement("script");
requireEl.defer = true;
requireEl.async = false;
requireEl.src = "$requireUrl";
// This attribute tells require JS what to load as main (defined below).
requireEl.setAttribute("data-main", "main_module.bootstrap");
document.head.appendChild(requireEl);

// Invoked by connected chrome debugger for hot reload/restart support.
window.\$hotReloadHook = function(modules) {
  return new Promise(function(resolve, reject) {
    if (modules == null) {
      reject();
    }
    // If no modules change, return immediately.
    if (modules.length == 0) {
      resolve();
    }
    var reloadCount = 0;
    for (var i = 0; i < modules.length; i++) {
      require.undef(modules[i]);
      require([modules[i]], function(module) {
        reloadCount += 1;
        // once we've reloaded every module, trigger the hot reload.
        if (reloadCount == modules.length) {
          require(["$entrypoint", "dart_sdk"], function(app, dart_sdk) {
            // See the doc comment under in generateMainModule.
            window.\$dartRunMain = app[Object.keys(app)[0]].main;
            window.\$hotReload(resolve);
          });
        }
      });
    }
  });
}
''';
}

/// Generate a synthetic main module which captures the application's main
/// method.
///
/// RE: Object.keys usage in app.main:
/// This attaches the main entrypoint and hot reload functionality to the window.
/// The app module will have a single property which contains the actual application
/// code. The property name is based off of the entrypoint that is generated, for example
/// the file `foo/bar/baz.dart` will generate a property named approximately
/// `foo__bar__baz`. Rather than attempt to guess, we assume the first property of
/// this object is the module.
String generateMainModule({@required String entrypoint}) {
  return '''/* ENTRYPOINT_EXTENTION_MARKER */
// baseUrlScript
var baseUrl = (function () {
  // Attempt to detect --precompiled mode for tests, and set the base url
  // appropriately, otherwise set it to '/'.
  var pathParts = location.pathname.split("/");
  if (pathParts[0] == "") {
    pathParts.shift();
  }
  if (pathParts.length > 1 && pathParts[1] == "test") {
    return "/" + pathParts.slice(0, 2).join("/") + "/";
  }
  // Attempt to detect base url using <base href> html tag
  // base href should start and end with "/"
  if (typeof document !== 'undefined') {
    var el = document.getElementsByTagName('base');
    if (el && el[0] && el[0].getAttribute("href") && el[0].getAttribute
    ("href").startsWith("/") && el[0].getAttribute("href").endsWith("/")){
      return el[0].getAttribute("href");
    }
  }
  // return default value
  return "/";
}());
$_currentDirectoryScript
// dart loader
if(!window.\$dartLoader) {
   window.\$dartLoader = {
     appDigests: _currentDirectory + 'basic.digests',
     moduleIdToUrl: new Map(),
     urlToModuleId: new Map(),
     rootDirectories: new Array(),
     // Used in package:build_runner/src/server/build_updates_client/hot_reload_client.dart
     moduleParentsGraph: new Map(),
     moduleLoadingErrorCallbacks: new Map(),
     forceLoadModule: function (moduleName, callback, onError) {
       if (typeof onError != 'undefined') {
         var errorCallbacks = \$dartLoader.moduleLoadingErrorCallbacks;
         if (!errorCallbacks.has(moduleName)) {
           errorCallbacks.set(moduleName, new Set());
         }
         errorCallbacks.get(moduleName).add(onError);
       }
       requirejs.undef(moduleName);
       requirejs([moduleName], function() {
         if (typeof onError != 'undefined') {
           errorCallbacks.get(moduleName).delete(onError);
         }
         if (typeof callback != 'undefined') {
           callback();
         }
       });
     },
     getModuleLibraries: null, // set up by _initializeTools
   };
}
let modulePaths = {};
let customModulePaths = {};
window.\$dartLoader.rootDirectories.push(window.location.origin + baseUrl);
for (let moduleName of Object.getOwnPropertyNames(modulePaths)) {
  let modulePath = modulePaths[moduleName];
  if (modulePath != moduleName) {
    customModulePaths[moduleName] = modulePath;
  }
  var src = window.location.origin + '/' + modulePath + '.js';
  if (window.\$dartLoader.moduleIdToUrl.has(moduleName)) {
    continue;
  }
  \$dartLoader.moduleIdToUrl.set(moduleName, src);
  \$dartLoader.urlToModuleId.set(src, moduleName);
}
// Create the main module loaded below.
define("main_module.bootstrap", ["$entrypoint", "dart_sdk"], function(app, dart_sdk) {
  dart_sdk.dart.setStartAsyncSynchronously(true);
  dart_sdk._debugger.registerDevtoolsFormatter();
  \$dartLoader.getModuleLibraries = dart_sdk.dart.getModuleLibraries;
  if (window.\$dartStackTraceUtility && !window.\$dartStackTraceUtility.ready) {
    window.\$dartStackTraceUtility.ready = true;
    let dart = dart_sdk.dart;
    window.\$dartStackTraceUtility.setSourceMapProvider(
      function(url) {
        url = url.replace(baseUrl, '/');
        var module = window.\$dartLoader.urlToModuleId.get(url);
        if (!module) {
          if (url.endsWith('dart_sdk.js')) {
            module = 'dart_sdk';
          } else {
            try {
              module = '/packages' + url.split('packages')[1].split('.')[0] + '.dart';
            } catch (e) {
              return null;
            }
          }
        }
        return dart.getSourceMap(module);
      });
  }
  if (typeof document != 'undefined') {
    window.postMessage({ type: "DDC_STATE_CHANGE", state: "start" }, "*");
  }
  dart_sdk._isolate_helper.startRootIsolate(() => {}, []);

  // See the generateMainModule doc comment.
  var child = {};
  child.main = app[Object.keys(app)[0]].main;
  if (window.\$hotReload == null) {
    window.\$hotReload = function(cb) {
      dart_sdk.developer.invokeExtension("ext.flutter.disassemble", "{}").then((_) => {
        dart_sdk.dart.hotRestart();
        window.\$dartRunMain();
        window.requestAnimationFrame(cb);
      });
    }
  }

  /* MAIN_EXTENSION_MARKER */
  child.main();
});

// Require JS configuration.
require.config({
  waitSeconds: 0,
});
''';
}