Console Logs And JavaScript Errors

Use browser.logs to capture what the page writes to the console and what JavaScript errors the browser reports. This is useful for failing tests on unexpected client-side errors, debugging flaky flows, or asserting that an app emitted a known log message.

Requires the default browser event connection. Console and JavaScript error capture requires enableBiDi: true (the default) and a browser that supports WebDriver BiDi. If you launch with enableBiDi: false, these methods throw a clear requires BiDi error.

Capture Timing

Capture is lazy by default. CraftDriver subscribes to log events the first time you touch browser.logs.onLog(), .onConsole(), .onError(), .on(), .waitForConsole(), or .waitForError().

Messages emitted before that first touch are not captured, so this can return an empty array:

await browser.navigateTo('https://example.com');
const messages = browser.logs.getMessages();

Start capture before the action that logs:

const warning = browser.logs.waitForConsole((msg) => msg.level === 'warn');

await browser.getByRole('button', { name: 'Show warning' }).click();
expect((await warning).text).toContain('Heads up');

Or start capture immediately at launch:

const browser = await Browser.launch({
  browserName: 'chrome',
  captureLogs: true,
});

Read Collected Messages

const messages = browser.logs.getMessages();

for (const msg of messages) {
  console.log(`[${msg.level}] ${msg.text}`);
}

Each console message has:

Property	Description
type	Always 'console'
level	'debug', 'info', 'warn', or 'error'
text	Message text
method	Console method, such as 'log', 'warn', or 'error'
args	Arguments passed to console.*
timestamp	When the message was logged
stackTrace	Optional stack frames

Filter by level:

const warnings = browser.logs.getLogsByLevel('warn');
const errors = browser.logs.getLogsByLevel('error');

Read JavaScript Errors

const errors = browser.logs.getErrors();

for (const error of errors) {
  console.log(`Error: ${error.text}`);
}

Each JavaScript error has:

Property	Description
type	Always 'javascript'
level	Always 'error'
text	Error message
timestamp	When the error occurred
stackTrace	Optional stack frames with function, URL, line, and column

Wait For A Log Or Error

const consoleMessage = browser.logs.waitForConsole((msg) => {
  return msg.level === 'info' && msg.text.includes('Saved');
});

await browser.getByRole('button', { name: 'Save' }).click();
expect((await consoleMessage).text).toContain('Saved');

const pageError = browser.logs.waitForError((error) => {
  return error.text.includes('Cannot read properties');
});

await browser.getByRole('button', { name: 'Trigger error' }).click();
expect((await pageError).text).toContain('Cannot read properties');

Subscribe In Real Time

const unsubscribeConsole = browser.logs.onConsole((msg) => {
  if (msg.level === 'error') {
    console.log('Console error:', msg.text);
  }
});

const unsubscribeErrors = browser.logs.onError((error) => {
  console.log('JavaScript error:', error.text);
});

// Later:
unsubscribeConsole();
unsubscribeErrors();

Fail On Unexpected Errors

await browser.navigateTo('https://example.com');
await browser.getByRole('button', { name: 'Run flow' }).click();

browser.logs.assertNoErrors();

You can also inspect errors yourself:

const errors = browser.logs.getErrors();
expect(errors).toHaveLength(0);

Other Helpers

Method	Description
onLog(handler)	Subscribe to all log messages
on(level, handler)	Subscribe to one level: debug, info, warn, or error
getLogs()	Return all captured console and JavaScript error messages
clearLogs()	Clear all collected console messages and errors
waitForConsole(predicate, timeout?)	Wait for a matching console message
waitForError(predicate?, timeout?)	Wait for a JavaScript error
assertNoErrors()	Throw if any JavaScript errors were captured