pkg/compiler/lib/src/js_emitter/main_call_stub_generator.dart

// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

library dart2js.js_emitter.main_call_stub_generator;

import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;

import '../elements/entities.dart';
import '../js/js.dart' as jsAst;
import '../js/js.dart' show js;

import 'code_emitter_task.dart' show Emitter;

class MainCallStubGenerator {
  static jsAst.Statement generateInvokeMain(
      Emitter emitter, FunctionEntity main) {
    jsAst.Expression mainCallClosure = emitter.staticFunctionAccess(main);
    jsAst.Expression currentScriptAccess =
        emitter.generateEmbeddedGlobalAccess(embeddedNames.CURRENT_SCRIPT);

    // This code finds the currently executing script by listening to the
    // onload event of all script tags and getting the first script which
    // finishes. Since onload is called immediately after execution this should
    // not substantially change execution order.
    return js.statement('''
      (function (callback) {
        if (typeof document === "undefined") {
          callback(null);
          return;
        }
        // When running as a content-script of a chrome-extension the
        // 'currentScript' is `null` (but not undefined).
        if (typeof document.currentScript != 'undefined') {
          callback(document.currentScript);
          return;
        }

        var scripts = document.scripts;
        function onLoad(event) {
          for (var i = 0; i < scripts.length; ++i) {
            scripts[i].removeEventListener("load", onLoad, false);
          }
          callback(event.target);
        }
        for (var i = 0; i < scripts.length; ++i) {
          scripts[i].addEventListener("load", onLoad, false);
        }
      })(function(currentScript) {
        #currentScript = currentScript;

        if (typeof dartMainRunner === "function") {
          dartMainRunner(#mainCallClosure, []);
        } else {
          #mainCallClosure([]);
        }
      })''', {
      'currentScript': currentScriptAccess,
      'mainCallClosure': mainCallClosure
    });
  }
}