Running JavaScript

Create a JavaScriptScriptEngine and give it to the browsing context. Navigate with NavigateAsync, which waits for the scripts that block the parser, then run the event loop:

using var engine = new JavaScriptScriptEngine(new JavaScriptScriptEngineOptions
{
    Timeout = TimeSpan.FromSeconds(5), // per script or callback
});

using var context = new BrowsingContext(new BrowsingContextOptions
{
    ScriptEngine = engine,
    DocumentLoader = DocumentLoader.Create(), // optional: external scripts, modules, fetch, XMLHttpRequest, WebSocket, EventSource...
    UnhandledScriptError = (_, error) => Console.Error.WriteLine(error),
    ConsoleMessage = (_, message) => Console.WriteLine(message.Text), // console.log(), console.count()...
});

var document = await context.NavigateAsync("https://example.com/", _ => """
    <title>Example</title>
    <ul id=list></ul>
    <script>
      setTimeout(() => document.getElementById('list').innerHTML = '<li>a<li>b', 100);
    </script>
    """);

// Run the tasks and the timers until there is nothing left
do { await context.EventLoop.RunUntilIdleAsync(); } while (await context.EventLoop.WaitForNextTimerAsync());

Assert.Equal("<li>a</li><li>b</li>", document.GetElementById("list")!.InnerHtml);

// Evaluate code in the realm of a window
var title = engine.Evaluate(context.Window, "document.title");
Assert.Equal("Example", title.AsString());

• The scripts run on the thread that runs the event loop, when the event loop runs their tasks: the inline scripts while the document is parsed, the timers and the event listeners when their tasks run.
• The external scripts and the modules are fetched by the DocumentLoader: without a loader, only the inline scripts run.
• The engine is disposable. Several browsing contexts can share it: each window is a realm of its own, with its own global object.
• A worker gets its own engine, with the same options, on its own thread.

Options

When a limit is exceeded, the script stops and its error is reported: see Running untrusted pages.

Console messages and errors

BrowsingContextOptions.ConsoleMessage receives the messages of console.log(), console.error() and the other methods of the console, formatted as the console of a browser formats them (ConsoleMessage.Text), with their level and their arguments. BrowsingContextOptions.UnhandledScriptError receives the errors that no script handled: the exceptions of the scripts and the rejected promises, with their message, their file and their position (ScriptError). The errors do not stop the page: the next scripts run, as in a browser.

Modules, workers and worklets

<script type="module">, import(), the import maps, the JSON and CSS modules, the dedicated and shared workers and the worklets are supported. Each worker runs its own event loop on its own thread; the event loop of the page waits for its workers in RunUntilIdleAsync().