yt_dlp/jsinterp.py

   1 import collections
   2 import contextlib
   3 import itertools
   4 import json
   5 import math
   6 import operator
   7 import re
   8
   9 from .utils import (
  10     NO_DEFAULT,
  11     ExtractorError,
  12     function_with_repr,
  13     js_to_json,
  14     remove_quotes,
  15     truncate_string,
  16     unified_timestamp,
  17     write_string,
  18 )
  19
  20
  21 def _js_bit_op(op):
  22     def zeroise(x):
  23         if x in (None, JS_Undefined):
  24             return 0
  25         with contextlib.suppress(TypeError):
  26             if math.isnan(x):  # NB: NaN cannot be checked by membership
  27                 return 0
  28         return x
  29
  30     def wrapped(a, b):
  31         return op(zeroise(a), zeroise(b)) & 0xffffffff
  32
  33     return wrapped
  34
  35
  36 def _js_arith_op(op):
  37
  38     def wrapped(a, b):
  39         if JS_Undefined in (a, b):
  40             return float('nan')
  41         return op(a or 0, b or 0)
  42
  43     return wrapped
  44
  45
  46 def _js_div(a, b):
  47     if JS_Undefined in (a, b) or not (a or b):
  48         return float('nan')
  49     return (a or 0) / b if b else float('inf')
  50
  51
  52 def _js_mod(a, b):
  53     if JS_Undefined in (a, b) or not b:
  54         return float('nan')
  55     return (a or 0) % b
  56
  57
  58 def _js_exp(a, b):
  59     if not b:
  60         return 1  # even 0 ** 0 !!
  61     elif JS_Undefined in (a, b):
  62         return float('nan')
  63     return (a or 0) ** b
  64
  65
  66 def _js_eq_op(op):
  67
  68     def wrapped(a, b):
  69         if {a, b} <= {None, JS_Undefined}:
  70             return op(a, a)
  71         return op(a, b)
  72
  73     return wrapped
  74
  75
  76 def _js_comp_op(op):
  77
  78     def wrapped(a, b):
  79         if JS_Undefined in (a, b):
  80             return False
  81         if isinstance(a, str) or isinstance(b, str):
  82             return op(str(a or 0), str(b or 0))
  83         return op(a or 0, b or 0)
  84
  85     return wrapped
  86
  87
  88 def _js_ternary(cndn, if_true=True, if_false=False):
  89     """Simulate JS's ternary operator (cndn?if_true:if_false)"""
  90     if cndn in (False, None, 0, '', JS_Undefined):
  91         return if_false
  92     with contextlib.suppress(TypeError):
  93         if math.isnan(cndn):  # NB: NaN cannot be checked by membership
  94             return if_false
  95     return if_true
  96
  97
  98 # Ref: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence
  99 _OPERATORS = {  # None => Defined in JSInterpreter._operator
 100     '?': None,
 101     '??': None,
 102     '||': None,
 103     '&&': None,
 104
 105     '|': _js_bit_op(operator.or_),
 106     '^': _js_bit_op(operator.xor),
 107     '&': _js_bit_op(operator.and_),
 108
 109     '===': operator.is_,
 110     '!==': operator.is_not,
 111     '==': _js_eq_op(operator.eq),
 112     '!=': _js_eq_op(operator.ne),
 113
 114     '<=': _js_comp_op(operator.le),
 115     '>=': _js_comp_op(operator.ge),
 116     '<': _js_comp_op(operator.lt),
 117     '>': _js_comp_op(operator.gt),
 118
 119     '>>': _js_bit_op(operator.rshift),
 120     '<<': _js_bit_op(operator.lshift),
 121
 122     '+': _js_arith_op(operator.add),
 123     '-': _js_arith_op(operator.sub),
 124
 125     '*': _js_arith_op(operator.mul),
 126     '%': _js_mod,
 127     '/': _js_div,
 128     '**': _js_exp,
 129 }
 130
 131 _COMP_OPERATORS = {'===', '!==', '==', '!=', '<=', '>=', '<', '>'}
 132
 133 _NAME_RE = r'[a-zA-Z_$][\w$]*'
 134 _MATCHING_PARENS = dict(zip(*zip('()', '{}', '[]')))
 135 _QUOTES = '\'"/'
 136
 137
 138 class JS_Undefined:
 139     pass
 140
 141
 142 class JS_Break(ExtractorError):
 143     def __init__(self):
 144         ExtractorError.__init__(self, 'Invalid break')
 145
 146
 147 class JS_Continue(ExtractorError):
 148     def __init__(self):
 149         ExtractorError.__init__(self, 'Invalid continue')
 150
 151
 152 class JS_Throw(ExtractorError):
 153     def __init__(self, e):
 154         self.error = e
 155         ExtractorError.__init__(self, f'Uncaught exception {e}')
 156
 157
 158 class LocalNameSpace(collections.ChainMap):
 159     def __setitem__(self, key, value):
 160         for scope in self.maps:
 161             if key in scope:
 162                 scope[key] = value
 163                 return
 164         self.maps[0][key] = value
 165
 166     def __delitem__(self, key):
 167         raise NotImplementedError('Deleting is not supported')
 168
 169
 170 class Debugger:
 171     import sys
 172     ENABLED = False and 'pytest' in sys.modules
 173
 174     @staticmethod
 175     def write(*args, level=100):
 176         write_string(f'[debug] JS: {"  " * (100 - level)}'
 177                      f'{" ".join(truncate_string(str(x), 50, 50) for x in args)}\n')
 178
 179     @classmethod
 180     def wrap_interpreter(cls, f):
 181         def interpret_statement(self, stmt, local_vars, allow_recursion, *args, **kwargs):
 182             if cls.ENABLED and stmt.strip():
 183                 cls.write(stmt, level=allow_recursion)
 184             try:
 185                 ret, should_ret = f(self, stmt, local_vars, allow_recursion, *args, **kwargs)
 186             except Exception as e:
 187                 if cls.ENABLED:
 188                     if isinstance(e, ExtractorError):
 189                         e = e.orig_msg
 190                     cls.write('=> Raises:', e, '<-|', stmt, level=allow_recursion)
 191                 raise
 192             if cls.ENABLED and stmt.strip():
 193                 if should_ret or repr(ret) != stmt:
 194                     cls.write(['->', '=>'][should_ret], repr(ret), '<-|', stmt, level=allow_recursion)
 195             return ret, should_ret
 196         return interpret_statement
 197
 198
 199 class JSInterpreter:
 200     __named_object_counter = 0
 201
 202     _RE_FLAGS = {
 203         # special knowledge: Python's re flags are bitmask values, current max 128
 204         # invent new bitmask values well above that for literal parsing
 205         # TODO: new pattern class to execute matches with these flags
 206         'd': 1024,  # Generate indices for substring matches
 207         'g': 2048,  # Global search
 208         'i': re.I,  # Case-insensitive search
 209         'm': re.M,  # Multi-line search
 210         's': re.S,  # Allows . to match newline characters
 211         'u': re.U,  # Treat a pattern as a sequence of unicode code points
 212         'y': 4096,  # Perform a "sticky" search that matches starting at the current position in the target string
 213     }
 214
 215     def __init__(self, code, objects=None):
 216         self.code, self._functions = code, {}
 217         self._objects = {} if objects is None else objects
 218
 219     class Exception(ExtractorError):  # noqa: A001
 220         def __init__(self, msg, expr=None, *args, **kwargs):
 221             if expr is not None:
 222                 msg = f'{msg.rstrip()} in: {truncate_string(expr, 50, 50)}'
 223             super().__init__(msg, *args, **kwargs)
 224
 225     def _named_object(self, namespace, obj):
 226         self.__named_object_counter += 1
 227         name = f'__yt_dlp_jsinterp_obj{self.__named_object_counter}'
 228         if callable(obj) and not isinstance(obj, function_with_repr):
 229             obj = function_with_repr(obj, f'F<{self.__named_object_counter}>')
 230         namespace[name] = obj
 231         return name
 232
 233     @classmethod
 234     def _regex_flags(cls, expr):
 235         flags = 0
 236         if not expr:
 237             return flags, expr
 238         for idx, ch in enumerate(expr):  # noqa: B007
 239             if ch not in cls._RE_FLAGS:
 240                 break
 241             flags |= cls._RE_FLAGS[ch]
 242         return flags, expr[idx + 1:]
 243
 244     @staticmethod
 245     def _separate(expr, delim=',', max_split=None):
 246         OP_CHARS = '+-*/%&|^=<>!,;{}:['
 247         if not expr:
 248             return
 249         counters = {k: 0 for k in _MATCHING_PARENS.values()}
 250         start, splits, pos, delim_len = 0, 0, 0, len(delim) - 1
 251         in_quote, escaping, after_op, in_regex_char_group = None, False, True, False
 252         for idx, char in enumerate(expr):
 253             if not in_quote and char in _MATCHING_PARENS:
 254                 counters[_MATCHING_PARENS[char]] += 1
 255             elif not in_quote and char in counters:
 256                 # Something's wrong if we get negative, but ignore it anyway
 257                 if counters[char]:
 258                     counters[char] -= 1
 259             elif not escaping:
 260                 if char in _QUOTES and in_quote in (char, None):
 261                     if in_quote or after_op or char != '/':
 262                         in_quote = None if in_quote and not in_regex_char_group else char
 263                 elif in_quote == '/' and char in '[]':
 264                     in_regex_char_group = char == '['
 265             escaping = not escaping and in_quote and char == '\\'
 266             in_unary_op = (not in_quote and not in_regex_char_group
 267                            and after_op not in (True, False) and char in '-+')
 268             after_op = char if (not in_quote and char in OP_CHARS) else (char.isspace() and after_op)
 269
 270             if char != delim[pos] or any(counters.values()) or in_quote or in_unary_op:
 271                 pos = 0
 272                 continue
 273             elif pos != delim_len:
 274                 pos += 1
 275                 continue
 276             yield expr[start: idx - delim_len]
 277             start, pos = idx + 1, 0
 278             splits += 1
 279             if max_split and splits >= max_split:
 280                 break
 281         yield expr[start:]
 282
 283     @classmethod
 284     def _separate_at_paren(cls, expr, delim=None):
 285         if delim is None:
 286             delim = expr and _MATCHING_PARENS[expr[0]]
 287         separated = list(cls._separate(expr, delim, 1))
 288         if len(separated) < 2:
 289             raise cls.Exception(f'No terminating paren {delim}', expr)
 290         return separated[0][1:].strip(), separated[1].strip()
 291
 292     def _operator(self, op, left_val, right_expr, expr, local_vars, allow_recursion):
 293         if op in ('||', '&&'):
 294             if (op == '&&') ^ _js_ternary(left_val):
 295                 return left_val  # short circuiting
 296         elif op == '??':
 297             if left_val not in (None, JS_Undefined):
 298                 return left_val
 299         elif op == '?':
 300             right_expr = _js_ternary(left_val, *self._separate(right_expr, ':', 1))
 301
 302         right_val = self.interpret_expression(right_expr, local_vars, allow_recursion)
 303         if not _OPERATORS.get(op):
 304             return right_val
 305
 306         try:
 307             return _OPERATORS[op](left_val, right_val)
 308         except Exception as e:
 309             raise self.Exception(f'Failed to evaluate {left_val!r} {op} {right_val!r}', expr, cause=e)
 310
 311     def _index(self, obj, idx, allow_undefined=False):
 312         if idx == 'length':
 313             return len(obj)
 314         try:
 315             return obj[int(idx)] if isinstance(obj, list) else obj[idx]
 316         except Exception as e:
 317             if allow_undefined:
 318                 return JS_Undefined
 319             raise self.Exception(f'Cannot get index {idx}', repr(obj), cause=e)
 320
 321     def _dump(self, obj, namespace):
 322         try:
 323             return json.dumps(obj)
 324         except TypeError:
 325             return self._named_object(namespace, obj)
 326
 327     @Debugger.wrap_interpreter
 328     def interpret_statement(self, stmt, local_vars, allow_recursion=100):
 329         if allow_recursion < 0:
 330             raise self.Exception('Recursion limit reached')
 331         allow_recursion -= 1
 332
 333         should_return = False
 334         sub_statements = list(self._separate(stmt, ';')) or ['']
 335         expr = stmt = sub_statements.pop().strip()
 336
 337         for sub_stmt in sub_statements:
 338             ret, should_return = self.interpret_statement(sub_stmt, local_vars, allow_recursion)
 339             if should_return:
 340                 return ret, should_return
 341
 342         m = re.match(r'(?P<var>(?:var|const|let)\s)|return(?:\s+|(?=["\'])|$)|(?P<throw>throw\s+)', stmt)
 343         if m:
 344             expr = stmt[len(m.group(0)):].strip()
 345             if m.group('throw'):
 346                 raise JS_Throw(self.interpret_expression(expr, local_vars, allow_recursion))
 347             should_return = not m.group('var')
 348         if not expr:
 349             return None, should_return
 350
 351         if expr[0] in _QUOTES:
 352             inner, outer = self._separate(expr, expr[0], 1)
 353             if expr[0] == '/':
 354                 flags, outer = self._regex_flags(outer)
 355                 # We don't support regex methods yet, so no point compiling it
 356                 inner = f'{inner}/{flags}'
 357                 # Avoid https://github.com/python/cpython/issues/74534
 358                 # inner = re.compile(inner[1:].replace('[[', r'[\['), flags=flags)
 359             else:
 360                 inner = json.loads(js_to_json(f'{inner}{expr[0]}', strict=True))
 361             if not outer:
 362                 return inner, should_return
 363             expr = self._named_object(local_vars, inner) + outer
 364
 365         if expr.startswith('new '):
 366             obj = expr[4:]
 367             if obj.startswith('Date('):
 368                 left, right = self._separate_at_paren(obj[4:])
 369                 date = unified_timestamp(
 370                     self.interpret_expression(left, local_vars, allow_recursion), False)
 371                 if date is None:
 372                     raise self.Exception(f'Failed to parse date {left!r}', expr)
 373                 expr = self._dump(int(date * 1000), local_vars) + right
 374             else:
 375                 raise self.Exception(f'Unsupported object {obj}', expr)
 376
 377         if expr.startswith('void '):
 378             left = self.interpret_expression(expr[5:], local_vars, allow_recursion)
 379             return None, should_return
 380
 381         if expr.startswith('{'):
 382             inner, outer = self._separate_at_paren(expr)
 383             # try for object expression (Map)
 384             sub_expressions = [list(self._separate(sub_expr.strip(), ':', 1)) for sub_expr in self._separate(inner)]
 385             if all(len(sub_expr) == 2 for sub_expr in sub_expressions):
 386                 def dict_item(key, val):
 387                     val = self.interpret_expression(val, local_vars, allow_recursion)
 388                     if re.match(_NAME_RE, key):
 389                         return key, val
 390                     return self.interpret_expression(key, local_vars, allow_recursion), val
 391
 392                 return dict(dict_item(k, v) for k, v in sub_expressions), should_return
 393
 394             inner, should_abort = self.interpret_statement(inner, local_vars, allow_recursion)
 395             if not outer or should_abort:
 396                 return inner, should_abort or should_return
 397             else:
 398                 expr = self._dump(inner, local_vars) + outer
 399
 400         if expr.startswith('('):
 401             inner, outer = self._separate_at_paren(expr)
 402             inner, should_abort = self.interpret_statement(inner, local_vars, allow_recursion)
 403             if not outer or should_abort:
 404                 return inner, should_abort or should_return
 405             else:
 406                 expr = self._dump(inner, local_vars) + outer
 407
 408         if expr.startswith('['):
 409             inner, outer = self._separate_at_paren(expr)
 410             name = self._named_object(local_vars, [
 411                 self.interpret_expression(item, local_vars, allow_recursion)
 412                 for item in self._separate(inner)])
 413             expr = name + outer
 414
 415         m = re.match(r'''(?x)
 416                 (?P<try>try)\s*\{|
 417                 (?P<if>if)\s*\(|
 418                 (?P<switch>switch)\s*\(|
 419                 (?P<for>for)\s*\(
 420                 ''', expr)
 421         md = m.groupdict() if m else {}
 422         if md.get('if'):
 423             cndn, expr = self._separate_at_paren(expr[m.end() - 1:])
 424             if_expr, expr = self._separate_at_paren(expr.lstrip())
 425             # TODO: "else if" is not handled
 426             else_expr = None
 427             m = re.match(r'else\s*{', expr)
 428             if m:
 429                 else_expr, expr = self._separate_at_paren(expr[m.end() - 1:])
 430             cndn = _js_ternary(self.interpret_expression(cndn, local_vars, allow_recursion))
 431             ret, should_abort = self.interpret_statement(
 432                 if_expr if cndn else else_expr, local_vars, allow_recursion)
 433             if should_abort:
 434                 return ret, True
 435
 436         if md.get('try'):
 437             try_expr, expr = self._separate_at_paren(expr[m.end() - 1:])
 438             err = None
 439             try:
 440                 ret, should_abort = self.interpret_statement(try_expr, local_vars, allow_recursion)
 441                 if should_abort:
 442                     return ret, True
 443             except Exception as e:
 444                 # XXX: This works for now, but makes debugging future issues very hard
 445                 err = e
 446
 447             pending = (None, False)
 448             m = re.match(fr'catch\s*(?P<err>\(\s*{_NAME_RE}\s*\))?\{{', expr)
 449             if m:
 450                 sub_expr, expr = self._separate_at_paren(expr[m.end() - 1:])
 451                 if err:
 452                     catch_vars = {}
 453                     if m.group('err'):
 454                         catch_vars[m.group('err')] = err.error if isinstance(err, JS_Throw) else err
 455                     catch_vars = local_vars.new_child(catch_vars)
 456                     err, pending = None, self.interpret_statement(sub_expr, catch_vars, allow_recursion)
 457
 458             m = re.match(r'finally\s*\{', expr)
 459             if m:
 460                 sub_expr, expr = self._separate_at_paren(expr[m.end() - 1:])
 461                 ret, should_abort = self.interpret_statement(sub_expr, local_vars, allow_recursion)
 462                 if should_abort:
 463                     return ret, True
 464
 465             ret, should_abort = pending
 466             if should_abort:
 467                 return ret, True
 468
 469             if err:
 470                 raise err
 471
 472         elif md.get('for'):
 473             constructor, remaining = self._separate_at_paren(expr[m.end() - 1:])
 474             if remaining.startswith('{'):
 475                 body, expr = self._separate_at_paren(remaining)
 476             else:
 477                 switch_m = re.match(r'switch\s*\(', remaining)  # FIXME: ?
 478                 if switch_m:
 479                     switch_val, remaining = self._separate_at_paren(remaining[switch_m.end() - 1:])
 480                     body, expr = self._separate_at_paren(remaining, '}')
 481                     body = 'switch(%s){%s}' % (switch_val, body)
 482                 else:
 483                     body, expr = remaining, ''
 484             start, cndn, increment = self._separate(constructor, ';')
 485             self.interpret_expression(start, local_vars, allow_recursion)
 486             while True:
 487                 if not _js_ternary(self.interpret_expression(cndn, local_vars, allow_recursion)):
 488                     break
 489                 try:
 490                     ret, should_abort = self.interpret_statement(body, local_vars, allow_recursion)
 491                     if should_abort:
 492                         return ret, True
 493                 except JS_Break:
 494                     break
 495                 except JS_Continue:
 496                     pass
 497                 self.interpret_expression(increment, local_vars, allow_recursion)
 498
 499         elif md.get('switch'):
 500             switch_val, remaining = self._separate_at_paren(expr[m.end() - 1:])
 501             switch_val = self.interpret_expression(switch_val, local_vars, allow_recursion)
 502             body, expr = self._separate_at_paren(remaining, '}')
 503             items = body.replace('default:', 'case default:').split('case ')[1:]
 504             for default in (False, True):
 505                 matched = False
 506                 for item in items:
 507                     case, stmt = (i.strip() for i in self._separate(item, ':', 1))
 508                     if default:
 509                         matched = matched or case == 'default'
 510                     elif not matched:
 511                         matched = (case != 'default'
 512                                    and switch_val == self.interpret_expression(case, local_vars, allow_recursion))
 513                     if not matched:
 514                         continue
 515                     try:
 516                         ret, should_abort = self.interpret_statement(stmt, local_vars, allow_recursion)
 517                         if should_abort:
 518                             return ret
 519                     except JS_Break:
 520                         break
 521                 if matched:
 522                     break
 523
 524         if md:
 525             ret, should_abort = self.interpret_statement(expr, local_vars, allow_recursion)
 526             return ret, should_abort or should_return
 527
 528         # Comma separated statements
 529         sub_expressions = list(self._separate(expr))
 530         if len(sub_expressions) > 1:
 531             for sub_expr in sub_expressions:
 532                 ret, should_abort = self.interpret_statement(sub_expr, local_vars, allow_recursion)
 533                 if should_abort:
 534                     return ret, True
 535             return ret, False
 536
 537         for m in re.finditer(rf'''(?x)
 538                 (?P<pre_sign>\+\+|--)(?P<var1>{_NAME_RE})|
 539                 (?P<var2>{_NAME_RE})(?P<post_sign>\+\+|--)''', expr):
 540             var = m.group('var1') or m.group('var2')
 541             start, end = m.span()
 542             sign = m.group('pre_sign') or m.group('post_sign')
 543             ret = local_vars[var]
 544             local_vars[var] += 1 if sign[0] == '+' else -1
 545             if m.group('pre_sign'):
 546                 ret = local_vars[var]
 547             expr = expr[:start] + self._dump(ret, local_vars) + expr[end:]
 548
 549         if not expr:
 550             return None, should_return
 551
 552         m = re.match(fr'''(?x)
 553             (?P<assign>
 554                 (?P<out>{_NAME_RE})(?:\[(?P<index>[^\]]+?)\])?\s*
 555                 (?P<op>{"|".join(map(re.escape, set(_OPERATORS) - _COMP_OPERATORS))})?
 556                 =(?!=)(?P<expr>.*)$
 557             )|(?P<return>
 558                 (?!if|return|true|false|null|undefined|NaN)(?P<name>{_NAME_RE})$
 559             )|(?P<indexing>
 560                 (?P<in>{_NAME_RE})\[(?P<idx>.+)\]$
 561             )|(?P<attribute>
 562                 (?P<var>{_NAME_RE})(?:(?P<nullish>\?)?\.(?P<member>[^(]+)|\[(?P<member2>[^\]]+)\])\s*
 563             )|(?P<function>
 564                 (?P<fname>{_NAME_RE})\((?P<args>.*)\)$
 565             )''', expr)
 566         if m and m.group('assign'):
 567             left_val = local_vars.get(m.group('out'))
 568
 569             if not m.group('index'):
 570                 local_vars[m.group('out')] = self._operator(
 571                     m.group('op'), left_val, m.group('expr'), expr, local_vars, allow_recursion)
 572                 return local_vars[m.group('out')], should_return
 573             elif left_val in (None, JS_Undefined):
 574                 raise self.Exception(f'Cannot index undefined variable {m.group("out")}', expr)
 575
 576             idx = self.interpret_expression(m.group('index'), local_vars, allow_recursion)
 577             if not isinstance(idx, (int, float)):
 578                 raise self.Exception(f'List index {idx} must be integer', expr)
 579             idx = int(idx)
 580             left_val[idx] = self._operator(
 581                 m.group('op'), self._index(left_val, idx), m.group('expr'), expr, local_vars, allow_recursion)
 582             return left_val[idx], should_return
 583
 584         elif expr.isdigit():
 585             return int(expr), should_return
 586
 587         elif expr == 'break':
 588             raise JS_Break
 589         elif expr == 'continue':
 590             raise JS_Continue
 591         elif expr == 'undefined':
 592             return JS_Undefined, should_return
 593         elif expr == 'NaN':
 594             return float('NaN'), should_return
 595
 596         elif m and m.group('return'):
 597             return local_vars.get(m.group('name'), JS_Undefined), should_return
 598
 599         with contextlib.suppress(ValueError):
 600             return json.loads(js_to_json(expr, strict=True)), should_return
 601
 602         if m and m.group('indexing'):
 603             val = local_vars[m.group('in')]
 604             idx = self.interpret_expression(m.group('idx'), local_vars, allow_recursion)
 605             return self._index(val, idx), should_return
 606
 607         for op in _OPERATORS:
 608             separated = list(self._separate(expr, op))
 609             right_expr = separated.pop()
 610             while True:
 611                 if op in '?<>*-' and len(separated) > 1 and not separated[-1].strip():
 612                     separated.pop()
 613                 elif not (separated and op == '?' and right_expr.startswith('.')):
 614                     break
 615                 right_expr = f'{op}{right_expr}'
 616                 if op != '-':
 617                     right_expr = f'{separated.pop()}{op}{right_expr}'
 618             if not separated:
 619                 continue
 620             left_val = self.interpret_expression(op.join(separated), local_vars, allow_recursion)
 621             return self._operator(op, left_val, right_expr, expr, local_vars, allow_recursion), should_return
 622
 623         if m and m.group('attribute'):
 624             variable, member, nullish = m.group('var', 'member', 'nullish')
 625             if not member:
 626                 member = self.interpret_expression(m.group('member2'), local_vars, allow_recursion)
 627             arg_str = expr[m.end():]
 628             if arg_str.startswith('('):
 629                 arg_str, remaining = self._separate_at_paren(arg_str)
 630             else:
 631                 arg_str, remaining = None, arg_str
 632
 633             def assertion(cndn, msg):
 634                 """ assert, but without risk of getting optimized out """
 635                 if not cndn:
 636                     raise self.Exception(f'{member} {msg}', expr)
 637
 638             def eval_method():
 639                 nonlocal member
 640
 641                 if (variable, member) == ('console', 'debug'):
 642                     if Debugger.ENABLED:
 643                         Debugger.write(self.interpret_expression(f'[{arg_str}]', local_vars, allow_recursion))
 644                     return
 645
 646                 types = {
 647                     'String': str,
 648                     'Math': float,
 649                     'Array': list,
 650                 }
 651                 obj = local_vars.get(variable, types.get(variable, NO_DEFAULT))
 652                 if obj is NO_DEFAULT:
 653                     if variable not in self._objects:
 654                         try:
 655                             self._objects[variable] = self.extract_object(variable)
 656                         except self.Exception:
 657                             if not nullish:
 658                                 raise
 659                     obj = self._objects.get(variable, JS_Undefined)
 660
 661                 if nullish and obj is JS_Undefined:
 662                     return JS_Undefined
 663
 664                 # Member access
 665                 if arg_str is None:
 666                     return self._index(obj, member, nullish)
 667
 668                 # Function call
 669                 argvals = [
 670                     self.interpret_expression(v, local_vars, allow_recursion)
 671                     for v in self._separate(arg_str)]
 672
 673                 # Fixup prototype call
 674                 if isinstance(obj, type) and member.startswith('prototype.'):
 675                     new_member, _, func_prototype = member.partition('.')[2].partition('.')
 676                     assertion(argvals, 'takes one or more arguments')
 677                     assertion(isinstance(argvals[0], obj), f'needs binding to type {obj}')
 678                     if func_prototype == 'call':
 679                         obj, *argvals = argvals
 680                     elif func_prototype == 'apply':
 681                         assertion(len(argvals) == 2, 'takes two arguments')
 682                         obj, argvals = argvals
 683                         assertion(isinstance(argvals, list), 'second argument needs to be a list')
 684                     else:
 685                         raise self.Exception(f'Unsupported Function method {func_prototype}', expr)
 686                     member = new_member
 687
 688                 if obj is str:
 689                     if member == 'fromCharCode':
 690                         assertion(argvals, 'takes one or more arguments')
 691                         return ''.join(map(chr, argvals))
 692                     raise self.Exception(f'Unsupported String method {member}', expr)
 693                 elif obj is float:
 694                     if member == 'pow':
 695                         assertion(len(argvals) == 2, 'takes two arguments')
 696                         return argvals[0] ** argvals[1]
 697                     raise self.Exception(f'Unsupported Math method {member}', expr)
 698
 699                 if member == 'split':
 700                     assertion(argvals, 'takes one or more arguments')
 701                     assertion(len(argvals) == 1, 'with limit argument is not implemented')
 702                     return obj.split(argvals[0]) if argvals[0] else list(obj)
 703                 elif member == 'join':
 704                     assertion(isinstance(obj, list), 'must be applied on a list')
 705                     assertion(len(argvals) == 1, 'takes exactly one argument')
 706                     return argvals[0].join(obj)
 707                 elif member == 'reverse':
 708                     assertion(not argvals, 'does not take any arguments')
 709                     obj.reverse()
 710                     return obj
 711                 elif member == 'slice':
 712                     assertion(isinstance(obj, (list, str)), 'must be applied on a list or string')
 713                     assertion(len(argvals) <= 2, 'takes between 0 and 2 arguments')
 714                     return obj[slice(*argvals, None)]
 715                 elif member == 'splice':
 716                     assertion(isinstance(obj, list), 'must be applied on a list')
 717                     assertion(argvals, 'takes one or more arguments')
 718                     index, how_many = map(int, ([*argvals, len(obj)])[:2])
 719                     if index < 0:
 720                         index += len(obj)
 721                     add_items = argvals[2:]
 722                     res = []
 723                     for _ in range(index, min(index + how_many, len(obj))):
 724                         res.append(obj.pop(index))
 725                     for i, item in enumerate(add_items):
 726                         obj.insert(index + i, item)
 727                     return res
 728                 elif member == 'unshift':
 729                     assertion(isinstance(obj, list), 'must be applied on a list')
 730                     assertion(argvals, 'takes one or more arguments')
 731                     for item in reversed(argvals):
 732                         obj.insert(0, item)
 733                     return obj
 734                 elif member == 'pop':
 735                     assertion(isinstance(obj, list), 'must be applied on a list')
 736                     assertion(not argvals, 'does not take any arguments')
 737                     if not obj:
 738                         return
 739                     return obj.pop()
 740                 elif member == 'push':
 741                     assertion(argvals, 'takes one or more arguments')
 742                     obj.extend(argvals)
 743                     return obj
 744                 elif member == 'forEach':
 745                     assertion(argvals, 'takes one or more arguments')
 746                     assertion(len(argvals) <= 2, 'takes at-most 2 arguments')
 747                     f, this = ([*argvals, ''])[:2]
 748                     return [f((item, idx, obj), {'this': this}, allow_recursion) for idx, item in enumerate(obj)]
 749                 elif member == 'indexOf':
 750                     assertion(argvals, 'takes one or more arguments')
 751                     assertion(len(argvals) <= 2, 'takes at-most 2 arguments')
 752                     idx, start = ([*argvals, 0])[:2]
 753                     try:
 754                         return obj.index(idx, start)
 755                     except ValueError:
 756                         return -1
 757                 elif member == 'charCodeAt':
 758                     assertion(isinstance(obj, str), 'must be applied on a string')
 759                     assertion(len(argvals) == 1, 'takes exactly one argument')
 760                     idx = argvals[0] if isinstance(argvals[0], int) else 0
 761                     if idx >= len(obj):
 762                         return None
 763                     return ord(obj[idx])
 764
 765                 idx = int(member) if isinstance(obj, list) else member
 766                 return obj[idx](argvals, allow_recursion=allow_recursion)
 767
 768             if remaining:
 769                 ret, should_abort = self.interpret_statement(
 770                     self._named_object(local_vars, eval_method()) + remaining,
 771                     local_vars, allow_recursion)
 772                 return ret, should_return or should_abort
 773             else:
 774                 return eval_method(), should_return
 775
 776         elif m and m.group('function'):
 777             fname = m.group('fname')
 778             argvals = [self.interpret_expression(v, local_vars, allow_recursion)
 779                        for v in self._separate(m.group('args'))]
 780             if fname in local_vars:
 781                 return local_vars[fname](argvals, allow_recursion=allow_recursion), should_return
 782             elif fname not in self._functions:
 783                 self._functions[fname] = self.extract_function(fname)
 784             return self._functions[fname](argvals, allow_recursion=allow_recursion), should_return
 785
 786         raise self.Exception(
 787             f'Unsupported JS expression {truncate_string(expr, 20, 20) if expr != stmt else ""}', stmt)
 788
 789     def interpret_expression(self, expr, local_vars, allow_recursion):
 790         ret, should_return = self.interpret_statement(expr, local_vars, allow_recursion)
 791         if should_return:
 792             raise self.Exception('Cannot return from an expression', expr)
 793         return ret
 794
 795     def extract_object(self, objname):
 796         _FUNC_NAME_RE = r'''(?:[a-zA-Z$0-9]+|"[a-zA-Z$0-9]+"|'[a-zA-Z$0-9]+')'''
 797         obj = {}
 798         obj_m = re.search(
 799             r'''(?x)
 800                 (?<!\.)%s\s*=\s*{\s*
 801                     (?P<fields>(%s\s*:\s*function\s*\(.*?\)\s*{.*?}(?:,\s*)?)*)
 802                 }\s*;
 803             ''' % (re.escape(objname), _FUNC_NAME_RE),
 804             self.code)
 805         if not obj_m:
 806             raise self.Exception(f'Could not find object {objname}')
 807         fields = obj_m.group('fields')
 808         # Currently, it only supports function definitions
 809         fields_m = re.finditer(
 810             r'''(?x)
 811                 (?P<key>%s)\s*:\s*function\s*\((?P<args>(?:%s|,)*)\){(?P<code>[^}]+)}
 812             ''' % (_FUNC_NAME_RE, _NAME_RE),
 813             fields)
 814         for f in fields_m:
 815             argnames = f.group('args').split(',')
 816             name = remove_quotes(f.group('key'))
 817             obj[name] = function_with_repr(self.build_function(argnames, f.group('code')), f'F<{name}>')
 818
 819         return obj
 820
 821     def extract_function_code(self, funcname):
 822         """ @returns argnames, code """
 823         func_m = re.search(
 824             r'''(?xs)
 825                 (?:
 826                     function\s+%(name)s|
 827                     [{;,]\s*%(name)s\s*=\s*function|
 828                     (?:var|const|let)\s+%(name)s\s*=\s*function
 829                 )\s*
 830                 \((?P<args>[^)]*)\)\s*
 831                 (?P<code>{.+})''' % {'name': re.escape(funcname)},
 832             self.code)
 833         if func_m is None:
 834             raise self.Exception(f'Could not find JS function "{funcname}"')
 835         code, _ = self._separate_at_paren(func_m.group('code'))
 836         return [x.strip() for x in func_m.group('args').split(',')], code
 837
 838     def extract_function(self, funcname):
 839         return function_with_repr(
 840             self.extract_function_from_code(*self.extract_function_code(funcname)),
 841             f'F<{funcname}>')
 842
 843     def extract_function_from_code(self, argnames, code, *global_stack):
 844         local_vars = {}
 845         while True:
 846             mobj = re.search(r'function\((?P<args>[^)]*)\)\s*{', code)
 847             if mobj is None:
 848                 break
 849             start, body_start = mobj.span()
 850             body, remaining = self._separate_at_paren(code[body_start - 1:])
 851             name = self._named_object(local_vars, self.extract_function_from_code(
 852                 [x.strip() for x in mobj.group('args').split(',')],
 853                 body, local_vars, *global_stack))
 854             code = code[:start] + name + remaining
 855         return self.build_function(argnames, code, local_vars, *global_stack)
 856
 857     def call_function(self, funcname, *args):
 858         return self.extract_function(funcname)(args)
 859
 860     def build_function(self, argnames, code, *global_stack):
 861         global_stack = list(global_stack) or [{}]
 862         argnames = tuple(argnames)
 863
 864         def resf(args, kwargs={}, allow_recursion=100):
 865             global_stack[0].update(itertools.zip_longest(argnames, args, fillvalue=None))
 866             global_stack[0].update(kwargs)
 867             var_stack = LocalNameSpace(*global_stack)
 868             ret, should_abort = self.interpret_statement(code.replace('\n', ' '), var_stack, allow_recursion - 1)
 869             if should_abort:
 870                 return ret
 871         return resf