apache/beam · error · ValueError

File " " is not a valid .js file.

Error message

File "{path}" is not a valid .js file.

What it means

The Beam YAML MapToFields transform raises this when a JavaScript UDF is specified via `path` but the file name does not end with '.js'. When neither `expression` nor `callable` is given, the transform loads the UDF from a file, and it only accepts files with a .js extension as a sanity check before reading them via FileSystems.

Solutions

1. Rename or point to the file so the path ends with '.js'.
2. If the code is TypeScript or needs bundling, compile/transpile it to plain JavaScript first and reference the .js output.
3. Alternatively inline the function via the `callable` or `expression` config option instead of `path`.

Example fix

# before
config:
  language: javascript
  path: my_udf.ts
  name: udf
# after
config:
  language: javascript
  path: my_udf.js
  name: udf

import os
assert path.endswith('.js'), f'File "{path}" is not a valid .js file.'
assert os.path.isfile(path.replace('gs://', '')) or path.startswith('gs://')

def is_js_udf_spec(cfg: dict) -> bool:
    return isinstance(cfg.get('path'), str) and cfg['path'].endswith('.js')

try:
    result = expand(cfg)
except ValueError as e:
    if 'is not a valid .js file' in str(e):
        cfg['path'] = fix_extension(cfg['path'], '.js')
        result = expand(cfg)
    else:
        raise

When it happens

Trigger: Calling _expand_javascript_mapping_func (via MapToFields with language: javascript) with config {'path': '...', 'name': '...'} where path lacks a .js suffix, e.g. a .ts file, extensionless file, or a directory path.

Common situations: Users point `path` at a TypeScript file, a bundled/minified file with a different extension, a file with wrong casing (.JS handled only if endswith matches exactly — '.JS' fails), or accidentally pass a directory or URL instead of a .js file.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• File " " is not a valid .py file.
• Unknown or unsupported atomic type
• Ambiguous expression type (perhaps missing quoting?)
• Ambiguous expression type (perhaps missing quoting?)
• An invalid input " " was specified in "fields".

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/bc44043d20f17584. Report an issue: GitHub.

Appendix: source

Thrown at sdks/python/apache_beam/yaml/yaml_mapping.py:276

        "quickjs-ng library is not installed.")

  if expression:
    source_code = f"""
    function udf(__row__) {{
      with (__row__) {{
        return ({expression});
      }}
    }}
    """
    user_entrypoint = 'udf'

  elif callable:
    source_code = f"var __udf__ = ({callable});"
    user_entrypoint = '__udf__'

  else:
    if not path.endswith('.js'):
      raise ValueError(f'File "{path}" is not a valid .js file.')
    udf_code = FileSystems.open(path).read().decode()
    source_code = udf_code
    user_entrypoint = name

  source_code += f"""
  function __convert_dates__(obj) {{
    if (obj && typeof obj === 'object') {{
      if (obj.__date__) {{
        return new Date(obj.value);
      }}
      for (var key in obj) {{
        if (obj.hasOwnProperty(key)) {{
          obj[key] = __convert_dates__(obj[key]);
        }}
      }}
    }}
    return obj;
  }}

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