demjson.decode()

import demjson
# from
js_obj = '{x:1, y:2, z:3}'
# to
py_obj = demjson.decode(js_obj)

chompjs.parse_js_object()

import chompjs
# from
js_obj = '{x:1, y:2, z:3}'
# to
py_obj = chompjs.parse_js_object(js_obj)

jsonnet.evaluate_snippet()

import json, _jsonnet
# from
js_obj = '{x:1, y:2, z:3}'
# to
py_obj = json.loads(_jsonnet.evaluate_snippet('snippet', js_obj))

ast.literal_eval()

import ast
# from
js_obj = "{'x':1, 'y':2, 'z':3}"
# to
py_obj = ast.literal_eval(js_obj)

Use json5

import json5
js_obj = '{x:1, y:2, z:3}'
py_obj = json5.loads(js_obj)
print(py_obj)
# output
# {'x': 1, 'y': 2, 'z': 3}

I'm facing the same problem this afternoon, and I finally found a quite good solution. That is JSON5.

The syntax of JSON5 is more similar to native JavaScript, so it can help you parse non-standard JSON objects.

You might want to check pyjson5 out.

If you have node available on the system, you can ask it to evaluate the javascript expression for you, and print the stringified result. The resulting JSON can then be fed to json.loads:

def evaluate_javascript(s):
 """Evaluate and stringify a javascript expression in node.js, and convert the
 resulting JSON to a Python object"""
 node = Popen(['node', '-'], stdin=PIPE, stdout=PIPE)
 stdout, _ = node.communicate(f'console.log(JSON.stringify({s}))'.encode('utf8'))
 return json.loads(stdout.decode('utf8'))

This will likely not work everywhere, but as a start, here's a simple regex that should convert the keys into quoted strings so you can pass into json.loads. Or is this what you're already doing?

In[70] : quote_keys_regex = r'([\{\s,])(\w+)(:)'
In[71] : re.sub(quote_keys_regex, r'1円"2円"3円', js_obj)
Out[71]: '{"x":1, "y":2, "z":3}'
In[72] : js_obj_2 = '{x:1, y:2, z:{k:3,j:2}}'
Int[73]: re.sub(quote_keys_regex, r'1円"2円"3円', js_obj_2)
Out[73]: '{"x":1, "y":2, "z":{"k":3,"j":2}}'

Not including objects

json.loads()

• json.loads() doesn't accept undefined, you have to change to null
• json.loads() only accept double quotes
  • {"foo": 1, "bar": null}

Use this if you are sure that your javascript code only have double quotes on key names.

import json
json_text = """{"foo": 1, "bar": undefined}"""
json_text = re.sub(r'("\s*:\s*)undefined(\s*[,}])', '\1円null\2円', json_text)
py_obj = json.loads(json_text)

ast.literal_eval()

• ast.literal_eval() doesn't accept undefined, you have to change to None
• ast.literal_eval() doesn't accept null, you have to change to None
• ast.literal_eval() doesn't accept true, you have to change to True
• ast.literal_eval() doesn't accept false, you have to change to False
• ast.literal_eval() accept single and double quotes
  • {"foo": 1, "bar": None} or {'foo': 1, 'bar': None}

import ast
js_obj = """{'foo': 1, 'bar': undefined}"""
js_obj = re.sub(r'([\'\"]\s*:\s*)undefined(\s*[,}])', '\1円None\2円', js_obj)
js_obj = re.sub(r'([\'\"]\s*:\s*)null(\s*[,}])', '\1円None\2円', js_obj)
js_obj = re.sub(r'([\'\"]\s*:\s*)NaN(\s*[,}])', '\1円None\2円', js_obj)
js_obj = re.sub(r'([\'\"]\s*:\s*)true(\s*[,}])', '\1円True\2円', js_obj)
js_obj = re.sub(r'([\'\"]\s*:\s*)false(\s*[,}])', '\1円False\2円', js_obj)
py_obj = ast.literal_eval(js_obj) 

Some answers here are outdated, so here's a speed comparison between json5, hjson, and chompjs. (ast.literal_eval and json.loads failed). Evaluated functions on a 1 MB js object to get a good sample. All 3 successes produced an identical dictionary.

# 100.00% - reference time
chompjs.parse_js_object(text)
# 666.65% - 7 times slower
hjson.loads(text)
# 60460.57% - 605 times slower
json5.loads(text)
# fail
ast.literal_eval(text)
json.loads(text)
# won't install on Python 3.11.9
demjson
jsonnet

• javascript
• python
• json
• web-scraping