What causes "browser focus is not supported by this browser backend" in jackwener/OpenCLI?

Switch to a backend that implements focus (Playwright/Puppeteer-based).

browser focus is not supported by this browser backend

Error message

browser focus is not supported by this browser backend

What it means

The `browser focus` command feature-detects `page.focus` on the active backend and throws this error when the method is absent. It signals that the connected browser backend cannot programmatically focus elements.

Source

Thrown at src/cli.ts:2127

      if (!resolvedTarget) return;
      const parsed = nthToResolveOpts(opts?.nth);
      if ('error' in parsed) {
        console.log(JSON.stringify({ error: { code: 'usage_error', message: parsed.error } }, null, 2));
        process.exitCode = EXIT_CODES.USAGE_ERROR;
        return;
      }
      const { matches_n, match_level } = await page.hover(resolvedTarget, parsed.opts);
      console.log(JSON.stringify({ hovered: true, target: resolvedTarget, matches_n, match_level }, null, 2));
    }));

  addBrowserTabOption(
    addSemanticLocatorOptions(browser.command('focus'))
      .argument('[target]', 'Numeric ref (from browser state / find), CSS selector, or omit when using --role/--name/etc.')
      .option('--nth <n>', 'When <target> is a multi-match CSS selector, pick the nth match (0-based)')
      .description('Focus an element — JSON envelope {focused, target, matches_n}'),
  )
    .action(browserAction(async (page, target, opts) => {
      if (typeof page.focus !== 'function') throw new Error('browser focus is not supported by this browser backend');
      const resolvedTarget = await resolveWriteTargetOrPrint(page, target, opts ?? {});
      if (!resolvedTarget) return;
      const parsed = nthToResolveOpts(opts?.nth);
      if ('error' in parsed) {
        console.log(JSON.stringify({ error: { code: 'usage_error', message: parsed.error } }, null, 2));
        process.exitCode = EXIT_CODES.USAGE_ERROR;
        return;
      }
      const { focused, matches_n, match_level } = await page.focus(resolvedTarget, parsed.opts);
      console.log(JSON.stringify({ focused, target: resolvedTarget, matches_n, match_level }, null, 2));
    }));

  addBrowserTabOption(
    addSemanticLocatorOptions(browser.command('dblclick'))
      .argument('[target]', 'Numeric ref (from browser state / find), CSS selector, or omit when using --role/--name/etc.')
      .option('--nth <n>', 'When <target> is a multi-match CSS selector, pick the nth match (0-based)')
      .description('Double-click element — JSON envelope {dblclicked, target, matches_n}'),
  )

View on GitHub (pinned to 49907e53dc)

Solutions

Switch to a backend that implements focus (Playwright/Puppeteer-based).
Fallback to `browser eval` calling `element.focus()` in page JavaScript.
Verify backend configuration flags point at a full automation driver.

Example fix

// before
browser --backend minimal focus '#email'
// after
browser --backend playwright focus '#email'
// or: browser eval "document.querySelector('#email').focus()"

Defensive patterns

Strategy: type-guard

Validate before calling

const page = await getBrowserPage();
if (typeof page.focus !== 'function') {
  throw new Error('Current backend cannot focus elements');
}

Type guard

function supportsFocus(page) {
  return typeof page?.focus === 'function';
}

Try / catch

try {
  await run(['browser', 'focus', sel]);
} catch (err) {
  if (String(err.message).includes('focus is not supported')) {
    await run(['browser', 'eval', `document.querySelector('${sel}').focus()`]);
  } else throw err;
}

Prevention

Check page.focus existence before focusing.
Prefer full-featured backends for form interaction workflows.
Use eval-based focus as a documented fallback.
Keep backend adapters updated.

When it happens

Trigger: Running `browser focus [target]` against a backend whose page object does not implement `focus` (`typeof page.focus !== 'function'`).

Common situations: Minimal/limited browser backend drivers, restricted automation adapters, or misconfigured backend selection in CLI options/env.

Related errors

AI-assisted analysis of jackwener/OpenCLI@49907e53dc (2026-08-29). Data as JSON: /api/errors/5d0e98194118c50c. Report an issue: GitHub.