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