browser-use/browser-use · error · ValueError

JavaScript code is empty after cleaning

Error message

JavaScript code is empty after cleaning

What it means

Raised by _fix_javascript_string when, after stripping whitespace, removing wrapper quotes, and un-escaping quotes, the resulting JavaScript string is empty. It is a guard so an empty expression is never sent to CDP.

Source

Thrown at browser_use/actor/page.py:188

		if (js_code.startswith('"') and js_code.endswith('"')) or (js_code.startswith("'") and js_code.endswith("'")):
			# Check if it's a wrapped string (not part of JS syntax)
			inner = js_code[1:-1]
			if inner.count('"') + inner.count("'") == 0 or '() =>' in inner:
				js_code = inner

		# 2. Only fix clearly escaped quotes that shouldn't be
		# But be very conservative - only if we're sure it's a Python string artifact
		if '\\"' in js_code and js_code.count('\\"') > js_code.count('"'):
			js_code = js_code.replace('\\"', '"')
		if "\\'" in js_code and js_code.count("\\'") > js_code.count("'"):
			js_code = js_code.replace("\\'", "'")

		# 3. Basic whitespace normalization only
		js_code = js_code.strip()

		# Final validation - ensure it's not empty
		if not js_code:
			raise ValueError('JavaScript code is empty after cleaning')

		return js_code

	async def screenshot(self, format: str = 'png', quality: int | None = None) -> str:
		"""Take a screenshot and return base64 encoded image.

		Args:
		    format: Image format ('jpeg', 'png', 'webp')
		    quality: Quality 0-100 for JPEG format

		Returns:
		    Base64-encoded image data
		"""
		session_id = await self._ensure_session()

		params: 'CaptureScreenshotParameters' = {'format': format}

		if quality is not None and format.lower() == 'jpeg':

View on GitHub (pinned to 6c73fced2f)

Solutions

1. Check the value before calling: if not js.strip(): raise/skip
2. Log the raw page_function at the call site to find where it became empty
3. If the code comes from an LLM action, add a non-empty constraint to the tool prompt

Example fix

# before
await page.evaluate(js_code)  # js_code may be ''

# after
if not js_code or not js_code.strip():
    raise ValueError('evaluate called with empty script')
await page.evaluate(js_code)

if not isinstance(js, str) or not js.strip():
    raise ValueError('refusing to evaluate empty script')

def is_nonempty_script(js) -> bool:
    return isinstance(js, str) and len(js.strip()) > 0

null

When it happens

Trigger: Passing an empty string or whitespace-only string to page.evaluate; passing a string that is only a pair of quotes ('""' or "''"), which the quote-unwrapping step strips to nothing; passing a variable that is None-ish or was truncated to empty by upstream code.

Common situations: LLM tool call produces an evaluate action with empty code; f-string interpolation that evaluates to empty (f'({expr})' with expr=''); copying a placeholder from docs without filling in the body.

Related errors

• JavaScript code must start with (...args) => format. Got: {p
• module '{__name__}' has no attribute '{name}'
• Failed to find DOM element based on backendNodeId, maybe pag
• Failed to click element: {js_e}
• JavaScript evaluation failed: {result["exceptionDetails"]}

AI-assisted analysis of browser-use/browser-use@6c73fced2f (2026-08-14). Data as JSON: /api/errors/d0521fa710001671. Report an issue: GitHub.