Table of Contents

Log Module

The Log module provides access to browser console logs and other logging events.

Overview

The Log module allows you to:

  • Capture console log messages
  • Monitor JavaScript errors
  • Track different log levels
  • Access log metadata

Accessing the Module

LogModule log = driver.Log;

Monitoring Console Logs

Basic Log Monitoring

// Add observer
driver.Log.OnEntryAdded.AddObserver((EntryAddedEventArgs e) =>
{
    Console.WriteLine($"[{e.Level}] {e.Text}");
});

// Subscribe to events
SubscribeCommandParameters subscribe =
    new SubscribeCommandParameters(driver.Log.OnEntryAdded.EventName);
await driver.Session.SubscribeAsync(subscribe);

// Navigate - console logs will be captured
await driver.BrowsingContext.NavigateAsync(
    new NavigateCommandParameters(contextId, "https://example.com"));

Log Entry Properties

driver.Log.OnEntryAdded.AddObserver((EntryAddedEventArgs e) =>
{
    Console.WriteLine($"Level: {e.Level}");          // Error, Warn, Info, Debug
    Console.WriteLine($"Text: {e.Text}");            // Log message
    Console.WriteLine($"Timestamp: {e.Timestamp}");  // When logged
    Console.WriteLine($"Type: {e.Type}");            // "console", "javascript"
    Console.WriteLine($"Method: {e.Method}");        // log, error, warn, etc.

    // Source is always present; its BrowsingContextId may be null for
    // realms not attached to a browsing context.
    Console.WriteLine($"Source: {e.Source.RealmId}");
    Console.WriteLine($"Context: {e.Source.BrowsingContextId}");

    if (e.StackTrace != null)
    {
        Console.WriteLine("Stack trace:");
        foreach (StackFrame frame in e.StackTrace.CallFrames)
        {
            Console.WriteLine($"  {frame.FunctionName} at {frame.Url}:{frame.LineNumber}");
        }
    }
});

Filtering by Log Level

Monitor Only Errors

driver.Log.OnEntryAdded.AddObserver((EntryAddedEventArgs e) =>
{
    if (e.Level == LogLevel.Error)
    {
        Console.WriteLine($"ERROR: {e.Text}");

        if (e.StackTrace != null)
        {
            foreach (StackFrame frame in e.StackTrace.CallFrames)
            {
                Console.WriteLine($"  at {frame.Url}:{frame.LineNumber}:{frame.ColumnNumber}");
            }
        }
    }
});

Monitor Warnings and Errors

driver.Log.OnEntryAdded.AddObserver((EntryAddedEventArgs e) =>
{
    if (e.Level == LogLevel.Error || e.Level == LogLevel.Warn)
    {
        Console.WriteLine($"[{e.Level}] {e.Text}");
    }
});

Log Types

Console Logs

These come from console.log(), console.error(), etc.:

driver.Log.OnEntryAdded.AddObserver((EntryAddedEventArgs e) =>
{
    if (e.Type == "console")
    {
        Console.WriteLine($"Console method: {e.Method}");
        Console.WriteLine($"Args: {e.Arguments?.Count ?? 0}");

        if (e.Arguments != null)
        {
            foreach (RemoteValue arg in e.Arguments)
            {
                Console.WriteLine($"  Type: {arg.Type}");
                Console.WriteLine($"  Value: {(arg as ValueHoldingRemoteValue)?.ValueObject ?? "null"}");
            }
        }
    }
});

JavaScript Errors

Uncaught JavaScript exceptions:

driver.Log.OnEntryAdded.AddObserver((EntryAddedEventArgs e) =>
{
    if (e.Type == "javascript" && e.Level == LogLevel.Error)
    {
        Console.WriteLine($"JavaScript Error: {e.Text}");
    }
});

Common Patterns

Collect All Logs

List<EntryAddedEventArgs> logs = new List<EntryAddedEventArgs>();

driver.Log.OnEntryAdded.AddObserver((EntryAddedEventArgs e) =>
{
    logs.Add(e);
});

SubscribeCommandParameters subscribe =
    new SubscribeCommandParameters(driver.Log.OnEntryAdded.EventName);
await driver.Session.SubscribeAsync(subscribe);

// Perform actions...

// Later, analyze logs
int errorCount = logs.Count(l => l.Level == LogLevel.Error);
int warnCount = logs.Count(l => l.Level == LogLevel.Warn);

Console.WriteLine($"Errors: {errorCount}, Warnings: {warnCount}");

Fail on JavaScript Errors

bool hasErrors = false;

driver.Log.OnEntryAdded.AddObserver((EntryAddedEventArgs e) =>
{
    if (e.Type == "javascript" && e.Level == LogLevel.Error)
    {
        hasErrors = true;
        Console.WriteLine($"JavaScript error detected: {e.Text}");
    }
});

SubscribeCommandParameters subscribe =
    new SubscribeCommandParameters(driver.Log.OnEntryAdded.EventName);
await driver.Session.SubscribeAsync(subscribe);

// Perform test actions...
await driver.BrowsingContext.NavigateAsync(navParams);

if (hasErrors)
{
    throw new Exception("Test failed due to JavaScript errors");
}

Log to File

string logFilePath = "browser-console.log";

driver.Log.OnEntryAdded.AddObserver(async (EntryAddedEventArgs e) =>
{
    string logLine = $"{e.Timestamp:yyyy-MM-dd HH:mm:ss.fff} [{e.Level}] {e.Text}\n";
    await File.AppendAllTextAsync(logFilePath, logLine);
},
ObservableEventHandlerOptions.RunHandlerAsynchronously);

Best Practices

  1. Subscribe early: Subscribe to log events before navigating
  2. Filter appropriately: Don't process every log if you only need errors
  3. Handle async logging: Use async handlers if writing to files or databases
  4. Store important logs: Keep error logs for debugging
  5. Test for errors: Fail tests if unexpected JavaScript errors occur

Next Steps

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