unclecode/crawl4ai · error · ValueError

Failed to compile C4A script: {str(e)}

Error message

Failed to compile C4A script: {str(e)}

What it means

Catch-all raised when compiling a js_source C4A script raises an unexpected exception that is not an ImportError and does not already look like a compilation error. The original exception text is embedded so the real cause (often a bug in the compiler or malformed input of an unexpected kind) is preserved.

Source

Thrown at crawl4ai/async_configs.py:1993

                        f"  Line {error.line}, Column {error.column}: {error.message}\n"
                        f"  Code: {error.source_line}"
                    )
                    if error.suggestions:
                        error_msg += f"\n  Suggestion: {error.suggestions[0].message}"
                        
                    raise ValueError(error_msg)
                    
            self.js_code = compiled_js
            
        except ImportError:
            raise ValueError(
                "C4A script compiler not available. "
                "Please ensure crawl4ai.script module is properly installed."
            )
        except Exception as e:
            # Re-raise with context
            if "compilation error" not in str(e).lower():
                raise ValueError(f"Failed to compile C4A script: {str(e)}")
            raise
    
    def is_match(self, url: str) -> bool:
        """Check if this config matches the given URL.
        
        Args:
            url: The URL to check against this config's matcher
            
        Returns:
            bool: True if this config should be used for the URL or if no matcher is set.
        """
        if self.url_matcher is None:
            return True
            
        if callable(self.url_matcher):
            # Single function matcher
            return self.url_matcher(url)
        

View on GitHub (pinned to 7e80152142)

Solutions

1. Read the embedded {str(e)} — it names the underlying failure
2. Ensure each js_source entry is a str (wrap Path reads: path.read_text())
3. Align versions: pip install --upgrade crawl4ai so core and script module match
4. If the error is a compiler bug, minimize the script and report it upstream

Example fix

// before
js_source=[Path("scripts/scroll.c4a")]  # Path object
// after
js_source=[Path("scripts/scroll.c4a").read_text()]

js_source = [s.read_text() if isinstance(s, Path) else s for s in js_source_list]
assert all(isinstance(s, str) and s for s in js_source)

def valid_js_source(scripts) -> bool:
    return all(isinstance(s, str) and s.strip() for s in scripts or [])

try:
    cfg = CrawlerRunConfig(js_source=scripts)
except ValueError as e:
    if "Failed to compile C4A script" in str(e):
        raise RuntimeError(f"C4A compiler failure: {e}") from e
    raise

When it happens

Trigger: Passing a non-string js_source entry (None, bytes, a Path); a version mismatch between crawl4ai core and crawl4ai.script internals; any runtime error inside the compiler itself.

Common situations: Reading scripts from files and passing Path objects; mixing crawl4ai package versions in one environment after a partial upgrade.

Related errors

• C4A Script compilation error (script {i+1}): Line {error.l
• extraction_strategy must be an instance of ExtractionStrateg
• chunking_strategy must be an instance of ChunkingStrategy
• link_preview_config must be LinkPreviewConfig object or dict
• virtual_scroll_config must be VirtualScrollConfig object or

AI-assisted analysis of unclecode/crawl4ai@7e80152142 (2026-08-14). Data as JSON: /api/errors/e38643fefc49b7af. Report an issue: GitHub.