Implement n-param descrambling using JSInterp

Fixes #29326, closes #29790, closes #30004, closes #30024, closes #30052,
closes #30088, closes #30097, closes #30102, closes #30109, closes #30119,
closes #30125, closes #30128, closes #30162, closes #30173, closes #30186,
closes #30192, closes #30221, closes #30239, closes #30539, closes #30552.

test/test_jsinterp.py

@@ -112,6 +112,72 @@ class TestJSInterpreter(unittest.TestCase):
         ''')
         self.assertEqual(jsi.call_function('z'), 5)
 
+    def test_for_loop(self):
+        # function x() { a=0; for (i=0; i-10; i++) {a++} a }
+        jsi = JSInterpreter('''
+        function x() { a=0; for (i=0; i-10; i = i + 1) {a++} a }
+        ''')
+        self.assertEqual(jsi.call_function('x'), 10)
+
+    def test_switch(self):
+        jsi = JSInterpreter('''
+        function x(f) { switch(f){
+            case 1:f+=1;
+            case 2:f+=2;
+            case 3:f+=3;break;
+            case 4:f+=4;
+            default:f=0;
+        } return f }
+        ''')
+        self.assertEqual(jsi.call_function('x', 1), 7)
+        self.assertEqual(jsi.call_function('x', 3), 6)
+        self.assertEqual(jsi.call_function('x', 5), 0)
+
+    def test_switch_default(self):
+        jsi = JSInterpreter('''
+        function x(f) { switch(f){
+            case 2: f+=2;
+            default: f-=1;
+            case 5:
+            case 6: f+=6;
+            case 0: break;
+            case 1: f+=1;
+        } return f }
+        ''')
+        self.assertEqual(jsi.call_function('x', 1), 2)
+        self.assertEqual(jsi.call_function('x', 5), 11)
+        self.assertEqual(jsi.call_function('x', 9), 14)
+
+    def test_try(self):
+        jsi = JSInterpreter('''
+        function x() { try{return 10} catch(e){return 5} }
+        ''')
+        self.assertEqual(jsi.call_function('x'), 10)
+
+    def test_for_loop_continue(self):
+        jsi = JSInterpreter('''
+        function x() { a=0; for (i=0; i-10; i++) { continue; a++ } a }
+        ''')
+        self.assertEqual(jsi.call_function('x'), 0)
+
+    def test_for_loop_break(self):
+        jsi = JSInterpreter('''
+        function x() { a=0; for (i=0; i-10; i++) { break; a++ } a }
+        ''')
+        self.assertEqual(jsi.call_function('x'), 0)
+
+    def test_literal_list(self):
+        jsi = JSInterpreter('''
+        function x() { [1, 2, "asdf", [5, 6, 7]][3] }
+        ''')
+        self.assertEqual(jsi.call_function('x'), [5, 6, 7])
+
+    def test_comma(self):
+        jsi = JSInterpreter('''
+        function x() { a=5; a -= 1, a+=3; return a }
+        ''')
+        self.assertEqual(jsi.call_function('x'), 7)
+
 
 if __name__ == '__main__':
     unittest.main()

test/test_youtube_lists.py

@@ -1,4 +1,5 @@
 #!/usr/bin/env python
+# -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
 # Allow direct execution
@@ -9,11 +10,10 @@ sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
 from test.helper import FakeYDL
 
-
 from youtube_dl.extractor import (
+    YoutubeIE,
     YoutubePlaylistIE,
     YoutubeTabIE,
-    YoutubeIE,
 )
 
 
@@ -25,38 +25,23 @@ class TestYoutubeLists(unittest.TestCase):
     def test_youtube_playlist_noplaylist(self):
         dl = FakeYDL()
         dl.params['noplaylist'] = True
+        dl.params['format'] = 'best'
         ie = YoutubePlaylistIE(dl)
         result = ie.extract('https://www.youtube.com/watch?v=FXxLjLQi3Fg&list=PLwiyx1dc3P2JR9N8gQaQN_BCvlSlap7re')
         self.assertEqual(result['_type'], 'url')
+        result = dl.extract_info(result['url'], download=False, ie_key=result.get('ie_key'), process=False)
         self.assertEqual(YoutubeIE().extract_id(result['url']), 'FXxLjLQi3Fg')
 
-    def test_youtube_course(self):
-        dl = FakeYDL()
-        ie = YoutubePlaylistIE(dl)
-        # TODO find a > 100 (paginating?) videos course
-        result = ie.extract('https://www.youtube.com/course?list=ECUl4u3cNGP61MdtwGTqZA0MreSaDybji8')
-        entries = list(result['entries'])
-        self.assertEqual(YoutubeIE().extract_id(entries[0]['url']), 'j9WZyLZCBzs')
-        self.assertEqual(len(entries), 25)
-        self.assertEqual(YoutubeIE().extract_id(entries[-1]['url']), 'rYefUsYuEp0')
-
     def test_youtube_mix(self):
         dl = FakeYDL()
-        ie = YoutubePlaylistIE(dl)
+        dl.params['format'] = 'best'
-        result = ie.extract('https://www.youtube.com/watch?v=W01L70IGBgE&index=2&list=RDOQpdSVF_k_w')
+        ie = YoutubeTabIE(dl)
-        entries = result['entries']
+        result = dl.extract_info('https://www.youtube.com/watch?v=uVJ0Il5WvbE&list=PLhQjrBD2T381k8ul4WQ8SQ165XqY149WW',
+                                 download=False, ie_key=ie.ie_key(), process=True)
+        entries = (result or {}).get('entries', [{'id': 'not_found', }])
         self.assertTrue(len(entries) >= 50)
         original_video = entries[0]
-        self.assertEqual(original_video['id'], 'OQpdSVF_k_w')
+        self.assertEqual(original_video['id'], 'uVJ0Il5WvbE')
-
-    def test_youtube_toptracks(self):
-        print('Skipping: The playlist page gives error 500')
-        return
-        dl = FakeYDL()
-        ie = YoutubePlaylistIE(dl)
-        result = ie.extract('https://www.youtube.com/playlist?list=MCUS')
-        entries = result['entries']
-        self.assertEqual(len(entries), 100)
 
     def test_youtube_flat_playlist_extraction(self):
         dl = FakeYDL()
@@ -67,7 +52,7 @@ class TestYoutubeLists(unittest.TestCase):
         entries = list(result['entries'])
         self.assertTrue(len(entries) == 1)
         video = entries[0]
-        self.assertEqual(video['_type'], 'url_transparent')
+        self.assertEqual(video['_type'], 'url')
         self.assertEqual(video['ie_key'], 'Youtube')
         self.assertEqual(video['id'], 'BaW_jenozKc')
         self.assertEqual(video['url'], 'BaW_jenozKc')

test/test_youtube_signature.py

@@ -14,9 +14,10 @@ import string
 
 from test.helper import FakeYDL
 from youtube_dl.extractor import YoutubeIE
+from youtube_dl.jsinterp import JSInterpreter
 from youtube_dl.compat import compat_str, compat_urlretrieve
 
-_TESTS = [
+_SIG_TESTS = [
     (
         'https://s.ytimg.com/yts/jsbin/html5player-vflHOr_nV.js',
         86,
@@ -64,6 +65,25 @@ _TESTS = [
     )
 ]
 
+_NSIG_TESTS = [
+    (
+        'https://www.youtube.com/s/player/9216d1f7/player_ias.vflset/en_US/base.js',
+        'SLp9F5bwjAdhE9F-', 'gWnb9IK2DJ8Q1w',
+    ),
+    (
+        'https://www.youtube.com/s/player/f8cb7a3b/player_ias.vflset/en_US/base.js',
+        'oBo2h5euWy6osrUt', 'ivXHpm7qJjJN',
+    ),
+    (
+        'https://www.youtube.com/s/player/2dfe380c/player_ias.vflset/en_US/base.js',
+        'oBo2h5euWy6osrUt', '3DIBbn3qdQ',
+    ),
+    (
+        'https://www.youtube.com/s/player/f1ca6900/player_ias.vflset/en_US/base.js',
+        'cu3wyu6LQn2hse', 'jvxetvmlI9AN9Q',
+    ),
+]
+
 
 class TestPlayerInfo(unittest.TestCase):
     def test_youtube_extract_player_info(self):
@@ -95,35 +115,54 @@ class TestSignature(unittest.TestCase):
             os.mkdir(self.TESTDATA_DIR)
 
 
+def t_factory(name, sig_func, url_pattern):
     def make_tfunc(url, sig_input, expected_sig):
-    m = re.match(r'.*-([a-zA-Z0-9_-]+)(?:/watch_as3|/html5player)?\.[a-z]+$', url)
+        m = url_pattern.match(url)
         assert m, '%r should follow URL format' % url
-    test_id = m.group(1)
+        test_id = m.group('id')
 
         def test_func(self):
-        basename = 'player-%s.js' % test_id
+            basename = 'player-{0}-{1}.js'.format(name, test_id)
             fn = os.path.join(self.TESTDATA_DIR, basename)
 
             if not os.path.exists(fn):
                 compat_urlretrieve(url, fn)
-
-        ydl = FakeYDL()
-        ie = YoutubeIE(ydl)
             with io.open(fn, encoding='utf-8') as testf:
                 jscode = testf.read()
-        func = ie._parse_sig_js(jscode)
+            self.assertEqual(sig_func(jscode, sig_input), expected_sig)
+
+        test_func.__name__ = str('test_{0}_js_{1}'.format(name, test_id))
+        setattr(TestSignature, test_func.__name__, test_func)
+    return make_tfunc
+
+
+def signature(jscode, sig_input):
+    func = YoutubeIE(FakeYDL())._parse_sig_js(jscode)
     src_sig = (
         compat_str(string.printable[:sig_input])
         if isinstance(sig_input, int) else sig_input)
-        got_sig = func(src_sig)
+    return func(src_sig)
-        self.assertEqual(got_sig, expected_sig)
-
-    test_func.__name__ = str('test_signature_js_' + test_id)
-    setattr(TestSignature, test_func.__name__, test_func)
 
 
-for test_spec in _TESTS:
+def n_sig(jscode, sig_input):
-    make_tfunc(*test_spec)
+    # Pending implementation of _extract_n_function_name() or similar in
+    # youtube.py, hard-code here
+    # funcname = YoutubeIE(FakeYDL())._extract_n_function_name(jscode)
+    import re
+    funcname = re.search(r'[=(,&|](\w+)\(\w+\),\w+\.set\("n",', jscode)
+    funcname = funcname and funcname.group(1)
+    return JSInterpreter(jscode).call_function(funcname, sig_input)
+
+
+make_sig_test = t_factory(
+    'signature', signature, re.compile(r'.*-(?P<id>[a-zA-Z0-9_-]+)(?:/watch_as3|/html5player)?\.[a-z]+$'))
+for test_spec in _SIG_TESTS:
+    make_sig_test(*test_spec)
+
+make_nsig_test = t_factory(
+    'nsig', n_sig, re.compile(r'.+/player/(?P<id>[a-zA-Z0-9_-]+)/.+.js$'))
+for test_spec in _NSIG_TESTS:
+    make_nsig_test(*test_spec)
 
 
 if __name__ == '__main__':

youtube_dl/compat.py

@@ -21,6 +21,10 @@ import subprocess
 import sys
 import xml.etree.ElementTree
 
+try:
+    import collections.abc as compat_collections_abc
+except ImportError:
+    import collections as compat_collections_abc
 
 try:
     import urllib.request as compat_urllib_request
@@ -2962,6 +2966,25 @@ else:
         compat_Struct = struct.Struct
 
 
+# compat_map/filter() returning an iterator, supposedly the
+# same versioning as for zip below
+try:
+    from future_builtins import map as compat_map
+except ImportError:
+    try:
+        from itertools import imap as compat_map
+    except ImportError:
+        compat_map = map
+
+try:
+    from future_builtins import filter as compat_filter
+except ImportError:
+    try:
+        from itertools import ifilter as compat_filter
+    except ImportError:
+        compat_filter = filter
+
+
 try:
     from future_builtins import zip as compat_zip
 except ImportError:  # not 2.6+ or is 3.x
@@ -3006,6 +3029,7 @@ __all__ = [
     'compat_b64decode',
     'compat_basestring',
     'compat_chr',
+    'compat_collections_abc',
     'compat_cookiejar',
     'compat_cookiejar_Cookie',
     'compat_cookies',
@@ -3015,6 +3039,7 @@ __all__ = [
     'compat_etree_fromstring',
     'compat_etree_register_namespace',
     'compat_expanduser',
+    'compat_filter',
     'compat_get_terminal_size',
     'compat_getenv',
     'compat_getpass',
@@ -3026,6 +3051,7 @@ __all__ = [
     'compat_integer_types',
     'compat_itertools_count',
     'compat_kwargs',
+    'compat_map',
     'compat_numeric_types',
     'compat_ord',
     'compat_os_name',

youtube_dl/extractor/youtube.py

@@ -13,6 +13,7 @@ from .common import InfoExtractor, SearchInfoExtractor
 from ..compat import (
     compat_chr,
     compat_HTTPError,
+    compat_map as map,
     compat_parse_qs,
     compat_str,
     compat_urllib_parse_unquote_plus,
@@ -1253,6 +1254,17 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
             raise ExtractorError('Cannot identify player %r' % player_url)
         return id_m.group('id')
 
+    def _get_player_code(self, video_id, player_url, player_id=None):
+        if not player_id:
+            player_id = self._extract_player_info(player_url)
+
+        if player_id not in self._code_cache:
+            self._code_cache[player_id] = self._download_webpage(
+                player_url, video_id,
+                note='Downloading player ' + player_id,
+                errnote='Download of %s failed' % player_url)
+        return self._code_cache[player_id]
+
     def _extract_signature_function(self, video_id, player_url, example_sig):
         player_id = self._extract_player_info(player_url)
 
@@ -1265,12 +1277,7 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
         if cache_spec is not None:
             return lambda s: ''.join(s[i] for i in cache_spec)
 
-        if player_id not in self._code_cache:
+        code = self._get_player_code(video_id, player_url, player_id)
-            self._code_cache[player_id] = self._download_webpage(
-                player_url, video_id,
-                note='Downloading player ' + player_id,
-                errnote='Download of %s failed' % player_url)
-        code = self._code_cache[player_id]
         res = self._parse_sig_js(code)
 
         test_string = ''.join(map(compat_chr, range(len(example_sig))))
@@ -1349,11 +1356,6 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
         if player_url is None:
             raise ExtractorError('Cannot decrypt signature without player_url')
 
-        if player_url.startswith('//'):
-            player_url = 'https:' + player_url
-        elif not re.match(r'https?://', player_url):
-            player_url = compat_urlparse.urljoin(
-                'https://www.youtube.com', player_url)
         try:
             player_id = (player_url, self._signature_cache_id(s))
             if player_id not in self._player_cache:
@@ -1370,6 +1372,88 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
             raise ExtractorError(
                 'Signature extraction failed: ' + tb, cause=e)
 
+    def _extract_player_url(self, webpage):
+        player_url = self._search_regex(
+            r'"(?:PLAYER_JS_URL|jsUrl)"\s*:\s*"([^"]+)"',
+            webpage or '', 'player URL', fatal=False)
+        if not player_url:
+            return
+        if player_url.startswith('//'):
+            player_url = 'https:' + player_url
+        elif not re.match(r'https?://', player_url):
+            player_url = compat_urlparse.urljoin(
+                'https://www.youtube.com', player_url)
+        return player_url
+
+    # from yt-dlp
+    # See also:
+    # 1. https://github.com/ytdl-org/youtube-dl/issues/29326#issuecomment-894619419
+    # 2. https://code.videolan.org/videolan/vlc/-/blob/4fb284e5af69aa9ac2100ccbdd3b88debec9987f/share/lua/playlist/youtube.lua#L116
+    # 3. https://github.com/ytdl-org/youtube-dl/issues/30097#issuecomment-950157377
+    def _extract_n_function_name(self, jscode):
+        return self._search_regex(
+            (r'\.get\("n"\)\)&&\(b=(?P<nfunc>[a-zA-Z0-9$]{3})\([a-zA-Z0-9]\)',),
+            jscode, 'Initial JS player n function name', group='nfunc')
+
+    def _extract_n_function(self, video_id, player_url):
+        player_id = self._extract_player_info(player_url)
+        func_code = self._downloader.cache.load('youtube-nsig', player_id)
+
+        if func_code:
+            jsi = JSInterpreter(func_code)
+        else:
+            player_id = self._extract_player_info(player_url)
+            jscode = self._get_player_code(video_id, player_url, player_id)
+            funcname = self._extract_n_function_name(jscode)
+            jsi = JSInterpreter(jscode)
+            func_code = jsi.extract_function_code(funcname)
+            self._downloader.cache.store('youtube-nsig', player_id, func_code)
+
+        if self._downloader.params.get('youtube_print_sig_code'):
+            self.to_screen('Extracted nsig function from {0}:\n{1}\n'.format(player_id, func_code[1]))
+
+        return lambda s: jsi.extract_function_from_code(*func_code)([s])
+
+    def _n_descramble(self, n_param, player_url, video_id):
+        """Compute the response to YT's "n" parameter challenge
+
+        Args:
+        n_param     -- challenge string that is the value of the
+                       URL's "n" query parameter
+        player_url  -- URL of YT player JS
+        video_id
+        """
+
+        sig_id = ('nsig_value', n_param)
+        if sig_id in self._player_cache:
+            return self._player_cache[sig_id]
+
+        try:
+            player_id = ('nsig', player_url)
+            if player_id not in self._player_cache:
+                self._player_cache[player_id] = self._extract_n_function(video_id, player_url)
+            func = self._player_cache[player_id]
+            self._player_cache[sig_id] = func(n_param)
+            if self._downloader.params.get('verbose', False):
+                self._downloader.to_screen('[debug] [%s] %s' % (self.IE_NAME, 'Decrypted nsig {0} => {1}'.format(n_param, self._player_cache[sig_id])))
+            return self._player_cache[sig_id]
+        except Exception as e:
+            raise ExtractorError(traceback.format_exc(), cause=e, video_id=video_id)
+
+    def _unthrottle_format_urls(self, video_id, player_url, formats):
+        for fmt in formats:
+            parsed_fmt_url = compat_urlparse.urlparse(fmt['url'])
+            qs = compat_urlparse.parse_qs(parsed_fmt_url.query)
+            n_param = qs.get('n')
+            if not n_param:
+                continue
+            n_param = n_param[-1]
+            n_response = self._n_descramble(n_param, player_url, video_id)
+            if n_response:
+                qs['n'] = [n_response]
+                fmt['url'] = compat_urlparse.urlunparse(
+                    parsed_fmt_url._replace(query=compat_urllib_parse_urlencode(qs, True)))
+
     def _mark_watched(self, video_id, player_response):
         playback_url = url_or_none(try_get(
             player_response,
@@ -1631,11 +1715,7 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
                 if not (sc and fmt_url and encrypted_sig):
                     continue
                 if not player_url:
-                    if not webpage:
+                    player_url = self._extract_player_url(webpage)
-                        continue
-                    player_url = self._search_regex(
-                        r'"(?:PLAYER_JS_URL|jsUrl)"\s*:\s*"([^"]+)"',
-                        webpage, 'player URL', fatal=False)
                 if not player_url:
                     continue
                 signature = self._decrypt_signature(sc['s'][0], video_id, player_url)
@@ -1781,6 +1861,10 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
         is_live = video_details.get('isLive')
         owner_profile_url = microformat.get('ownerProfileUrl')
 
+        if not player_url:
+            player_url = self._extract_player_url(webpage)
+        self._unthrottle_format_urls(video_id, player_url, formats)
+
         info = {
             'id': video_id,
             'title': self._live_title(video_title) if is_live else video_title,

youtube_dl/jsinterp.py

@@ -8,6 +8,16 @@ from .utils import (
     ExtractorError,
     remove_quotes,
 )
+from .compat import (
+    compat_collections_abc,
+    compat_str,
+)
+MutableMapping = compat_collections_abc.MutableMapping
+
+
+class Nonlocal:
+    pass
+
 
 _OPERATORS = [
     ('|', operator.or_),
@@ -22,10 +32,56 @@ _OPERATORS = [
     ('*', operator.mul),
 ]
 _ASSIGN_OPERATORS = [(op + '=', opfunc) for op, opfunc in _OPERATORS]
-_ASSIGN_OPERATORS.append(('=', lambda cur, right: right))
+_ASSIGN_OPERATORS.append(('=', (lambda cur, right: right)))
 
 _NAME_RE = r'[a-zA-Z_$][a-zA-Z_$0-9]*'
 
+_MATCHING_PARENS = dict(zip(*zip('()', '{}', '[]')))
+
+
+class JS_Break(ExtractorError):
+    def __init__(self):
+        ExtractorError.__init__(self, 'Invalid break')
+
+
+class JS_Continue(ExtractorError):
+    def __init__(self):
+        ExtractorError.__init__(self, 'Invalid continue')
+
+
+class LocalNameSpace(MutableMapping):
+    def __init__(self, *stack):
+        self.stack = tuple(stack)
+
+    def __getitem__(self, key):
+        for scope in self.stack:
+            if key in scope:
+                return scope[key]
+        raise KeyError(key)
+
+    def __setitem__(self, key, value):
+        for scope in self.stack:
+            if key in scope:
+                scope[key] = value
+                break
+        else:
+            self.stack[0][key] = value
+        return value
+
+    def __delitem__(self, key):
+        raise NotImplementedError('Deleting is not supported')
+
+    def __iter__(self):
+        for scope in self.stack:
+            for scope_item in iter(scope):
+                yield scope_item
+
+    def __len__(self, key):
+        return len(iter(self))
+
+    def __repr__(self):
+        return 'LocalNameSpace%s' % (self.stack, )
+
 
 class JSInterpreter(object):
     def __init__(self, code, objects=None):
@@ -34,11 +90,56 @@ class JSInterpreter(object):
         self.code = code
         self._functions = {}
         self._objects = objects
+        self.__named_object_counter = 0
+
+    def _named_object(self, namespace, obj):
+        self.__named_object_counter += 1
+        name = '__youtube_dl_jsinterp_obj%s' % (self.__named_object_counter, )
+        namespace[name] = obj
+        return name
+
+    @staticmethod
+    def _separate(expr, delim=',', max_split=None):
+        if not expr:
+            return
+        counters = {k: 0 for k in _MATCHING_PARENS.values()}
+        start, splits, pos, delim_len = 0, 0, 0, len(delim) - 1
+        for idx, char in enumerate(expr):
+            if char in _MATCHING_PARENS:
+                counters[_MATCHING_PARENS[char]] += 1
+            elif char in counters:
+                counters[char] -= 1
+            if char != delim[pos] or any(counters.values()):
+                pos = 0
+                continue
+            elif pos != delim_len:
+                pos += 1
+                continue
+            yield expr[start: idx - delim_len]
+            start, pos = idx + 1, 0
+            splits += 1
+            if max_split and splits >= max_split:
+                break
+        yield expr[start:]
+
+    @staticmethod
+    def _separate_at_paren(expr, delim):
+        separated = list(JSInterpreter._separate(expr, delim, 1))
+        if len(separated) < 2:
+            raise ExtractorError('No terminating paren {0} in {1}'.format(delim, expr))
+        return separated[0][1:].strip(), separated[1].strip()
 
     def interpret_statement(self, stmt, local_vars, allow_recursion=100):
         if allow_recursion < 0:
             raise ExtractorError('Recursion limit reached')
 
+        sub_statements = list(self._separate(stmt, ';'))
+        stmt = (sub_statements or ['']).pop()
+        for sub_stmt in sub_statements:
+            ret, should_abort = self.interpret_statement(sub_stmt, local_vars, allow_recursion - 1)
+            if should_abort:
+                return ret
+
         should_abort = False
         stmt = stmt.lstrip()
         stmt_m = re.match(r'var\s', stmt)
@@ -61,25 +162,124 @@ class JSInterpreter(object):
         if expr == '':  # Empty expression
             return None
 
+        if expr.startswith('{'):
+            inner, outer = self._separate_at_paren(expr, '}')
+            inner, should_abort = self.interpret_statement(inner, local_vars, allow_recursion - 1)
+            if not outer or should_abort:
+                return inner
+            else:
+                expr = json.dumps(inner) + outer
+
         if expr.startswith('('):
-            parens_count = 0
+            inner, outer = self._separate_at_paren(expr, ')')
-            for m in re.finditer(r'[()]', expr):
+            inner = self.interpret_expression(inner, local_vars, allow_recursion)
-                if m.group(0) == '(':
+            if not outer:
-                    parens_count += 1
+                return inner
             else:
-                    parens_count -= 1
+                expr = json.dumps(inner) + outer
-                    if parens_count == 0:
+
-                        sub_expr = expr[1:m.start()]
+        if expr.startswith('['):
-                        sub_result = self.interpret_expression(
+            inner, outer = self._separate_at_paren(expr, ']')
-                            sub_expr, local_vars, allow_recursion)
+            name = self._named_object(local_vars, [
-                        remaining_expr = expr[m.end():].strip()
+                self.interpret_expression(item, local_vars, allow_recursion)
-                        if not remaining_expr:
+                for item in self._separate(inner)])
-                            return sub_result
+            expr = name + outer
+
+        m = re.match(r'try\s*', expr)
+        if m:
+            if expr[m.end()] == '{':
+                try_expr, expr = self._separate_at_paren(expr[m.end():], '}')
             else:
-                            expr = json.dumps(sub_result) + remaining_expr
+                try_expr, expr = expr[m.end() - 1:], ''
+            ret, should_abort = self.interpret_statement(try_expr, local_vars, allow_recursion - 1)
+            if should_abort:
+                return ret
+            return self.interpret_statement(expr, local_vars, allow_recursion - 1)[0]
+
+        m = re.match(r'(?:(?P<catch>catch)|(?P<for>for)|(?P<switch>switch))\s*\(', expr)
+        md = m.groupdict() if m else {}
+        if md.get('catch'):
+            # We ignore the catch block
+            _, expr = self._separate_at_paren(expr, '}')
+            return self.interpret_statement(expr, local_vars, allow_recursion - 1)[0]
+
+        elif md.get('for'):
+            def raise_constructor_error(c):
+                raise ExtractorError(
+                    'Premature return in the initialization of a for loop in {0!r}'.format(c))
+
+            constructor, remaining = self._separate_at_paren(expr[m.end() - 1:], ')')
+            if remaining.startswith('{'):
+                body, expr = self._separate_at_paren(remaining, '}')
+            else:
+                m = re.match(r'switch\s*\(', remaining)  # FIXME
+                if m:
+                    switch_val, remaining = self._separate_at_paren(remaining[m.end() - 1:], ')')
+                    body, expr = self._separate_at_paren(remaining, '}')
+                    body = 'switch(%s){%s}' % (switch_val, body)
+                else:
+                    body, expr = remaining, ''
+            start, cndn, increment = self._separate(constructor, ';')
+            if self.interpret_statement(start, local_vars, allow_recursion - 1)[1]:
+                raise_constructor_error(constructor)
+            while True:
+                if not self.interpret_expression(cndn, local_vars, allow_recursion):
                     break
-            else:
+                try:
-                raise ExtractorError('Premature end of parens in %r' % expr)
+                    ret, should_abort = self.interpret_statement(body, local_vars, allow_recursion - 1)
+                    if should_abort:
+                        return ret
+                except JS_Break:
+                    break
+                except JS_Continue:
+                    pass
+                if self.interpret_statement(increment, local_vars, allow_recursion - 1)[1]:
+                    raise_constructor_error(constructor)
+            return self.interpret_statement(expr, local_vars, allow_recursion - 1)[0]
+
+        elif md.get('switch'):
+            switch_val, remaining = self._separate_at_paren(expr[m.end() - 1:], ')')
+            switch_val = self.interpret_expression(switch_val, local_vars, allow_recursion)
+            body, expr = self._separate_at_paren(remaining, '}')
+            items = body.replace('default:', 'case default:').split('case ')[1:]
+            for default in (False, True):
+                matched = False
+                for item in items:
+                    case, stmt = [i.strip() for i in self._separate(item, ':', 1)]
+                    if default:
+                        matched = matched or case == 'default'
+                    elif not matched:
+                        matched = (case != 'default'
+                                   and switch_val == self.interpret_expression(case, local_vars, allow_recursion))
+                    if not matched:
+                        continue
+                    try:
+                        ret, should_abort = self.interpret_statement(stmt, local_vars, allow_recursion - 1)
+                        if should_abort:
+                            return ret
+                    except JS_Break:
+                        break
+                if matched:
+                    break
+            return self.interpret_statement(expr, local_vars, allow_recursion - 1)[0]
+
+        # Comma separated statements
+        sub_expressions = list(self._separate(expr))
+        expr = sub_expressions.pop().strip() if sub_expressions else ''
+        for sub_expr in sub_expressions:
+            self.interpret_expression(sub_expr, local_vars, allow_recursion)
+
+        for m in re.finditer(r'''(?x)
+                (?P<pre_sign>\+\+|--)(?P<var1>%(_NAME_RE)s)|
+                (?P<var2>%(_NAME_RE)s)(?P<post_sign>\+\+|--)''' % globals(), expr):
+            var = m.group('var1') or m.group('var2')
+            start, end = m.span()
+            sign = m.group('pre_sign') or m.group('post_sign')
+            ret = local_vars[var]
+            local_vars[var] += 1 if sign[0] == '+' else -1
+            if m.group('pre_sign'):
+                ret = local_vars[var]
+            expr = expr[:start] + json.dumps(ret) + expr[end:]
 
         for op, opfunc in _ASSIGN_OPERATORS:
             m = re.match(r'''(?x)
@@ -88,14 +288,13 @@ class JSInterpreter(object):
                 (?P<expr>.*)$''' % (_NAME_RE, re.escape(op)), expr)
             if not m:
                 continue
-            right_val = self.interpret_expression(
+            right_val = self.interpret_expression(m.group('expr'), local_vars, allow_recursion)
-                m.group('expr'), local_vars, allow_recursion - 1)
 
             if m.groupdict().get('index'):
                 lvar = local_vars[m.group('out')]
-                idx = self.interpret_expression(
+                idx = self.interpret_expression(m.group('index'), local_vars, allow_recursion)
-                    m.group('index'), local_vars, allow_recursion)
+                if not isinstance(idx, int):
-                assert isinstance(idx, int)
+                    raise ExtractorError('List indices must be integers: %s' % (idx, ))
                 cur = lvar[idx]
                 val = opfunc(cur, right_val)
                 lvar[idx] = val
@@ -109,8 +308,13 @@ class JSInterpreter(object):
         if expr.isdigit():
             return int(expr)
 
+        if expr == 'break':
+            raise JS_Break()
+        elif expr == 'continue':
+            raise JS_Continue()
+
         var_m = re.match(
-            r'(?!if|return|true|false)(?P<name>%s)$' % _NAME_RE,
+            r'(?!if|return|true|false|null)(?P<name>%s)$' % _NAME_RE,
             expr)
         if var_m:
             return local_vars[var_m.group('name')]
@@ -124,19 +328,53 @@ class JSInterpreter(object):
             r'(?P<in>%s)\[(?P<idx>.+)\]$' % _NAME_RE, expr)
         if m:
             val = local_vars[m.group('in')]
-            idx = self.interpret_expression(
+            idx = self.interpret_expression(m.group('idx'), local_vars, allow_recursion)
-                m.group('idx'), local_vars, allow_recursion - 1)
             return val[idx]
 
+        def raise_expr_error(where, op, exp):
+            raise ExtractorError('Premature {0} return of {1} in {2!r}'.format(where, op, exp))
+
+        for op, opfunc in _OPERATORS:
+            separated = list(self._separate(expr, op))
+            if len(separated) < 2:
+                continue
+            right_val = separated.pop()
+            left_val = op.join(separated)
+            left_val, should_abort = self.interpret_statement(
+                left_val, local_vars, allow_recursion - 1)
+            if should_abort:
+                raise_expr_error('left-side', op, expr)
+            right_val, should_abort = self.interpret_statement(
+                right_val, local_vars, allow_recursion - 1)
+            if should_abort:
+                raise_expr_error('right-side', op, expr)
+            return opfunc(left_val or 0, right_val)
+
         m = re.match(
-            r'(?P<var>%s)(?:\.(?P<member>[^(]+)|\[(?P<member2>[^]]+)\])\s*(?:\(+(?P<args>[^()]*)\))?$' % _NAME_RE,
+            r'(?P<var>%s)(?:\.(?P<member>[^(]+)|\[(?P<member2>[^]]+)\])\s*' % _NAME_RE,
             expr)
         if m:
             variable = m.group('var')
-            member = remove_quotes(m.group('member') or m.group('member2'))
+            nl = Nonlocal()
-            arg_str = m.group('args')
 
-            if variable in local_vars:
+            nl.member = remove_quotes(m.group('member') or m.group('member2'))
+            arg_str = expr[m.end():]
+            if arg_str.startswith('('):
+                arg_str, remaining = self._separate_at_paren(arg_str, ')')
+            else:
+                arg_str, remaining = None, arg_str
+
+            def assertion(cndn, msg):
+                """ assert, but without risk of getting optimized out """
+                if not cndn:
+                    raise ExtractorError('{0} {1}: {2}'.format(nl.member, msg, expr))
+
+            def eval_method():
+                # nonlocal member
+                member = nl.member
+                if variable == 'String':
+                    obj = compat_str
+                elif variable in local_vars:
                     obj = local_vars[variable]
                 else:
                     if variable not in self._objects:
@@ -149,65 +387,101 @@ class JSInterpreter(object):
                         return len(obj)
                     return obj[member]
 
-            assert expr.endswith(')')
                 # Function call
-            if arg_str == '':
+                argvals = [
-                argvals = tuple()
-            else:
-                argvals = tuple([
                     self.interpret_expression(v, local_vars, allow_recursion)
-                    for v in arg_str.split(',')])
+                    for v in self._separate(arg_str)]
+
+                if obj == compat_str:
+                    if member == 'fromCharCode':
+                        assertion(argvals, 'takes one or more arguments')
+                        return ''.join(map(chr, argvals))
+                    raise ExtractorError('Unsupported string method %s' % (member, ))
 
                 if member == 'split':
-                assert argvals == ('',)
+                    assertion(argvals, 'takes one or more arguments')
+                    assertion(argvals == [''], 'with arguments is not implemented')
                     return list(obj)
-            if member == 'join':
+                elif member == 'join':
-                assert len(argvals) == 1
+                    assertion(isinstance(obj, list), 'must be applied on a list')
+                    assertion(len(argvals) == 1, 'takes exactly one argument')
                     return argvals[0].join(obj)
-            if member == 'reverse':
+                elif member == 'reverse':
-                assert len(argvals) == 0
+                    assertion(not argvals, 'does not take any arguments')
                     obj.reverse()
                     return obj
-            if member == 'slice':
+                elif member == 'slice':
-                assert len(argvals) == 1
+                    assertion(isinstance(obj, list), 'must be applied on a list')
+                    assertion(len(argvals) == 1, 'takes exactly one argument')
                     return obj[argvals[0]:]
-            if member == 'splice':
+                elif member == 'splice':
-                assert isinstance(obj, list)
+                    assertion(isinstance(obj, list), 'must be applied on a list')
-                index, howMany = argvals
+                    assertion(argvals, 'takes one or more arguments')
+                    index, howMany = map(int, (argvals + [len(obj)])[:2])
+                    if index < 0:
+                        index += len(obj)
+                    add_items = argvals[2:]
                     res = []
                     for i in range(index, min(index + howMany, len(obj))):
                         res.append(obj.pop(index))
+                    for i, item in enumerate(add_items):
+                        obj.insert(index + i, item)
                     return res
+                elif member == 'unshift':
+                    assertion(isinstance(obj, list), 'must be applied on a list')
+                    assertion(argvals, 'takes one or more arguments')
+                    for item in reversed(argvals):
+                        obj.insert(0, item)
+                    return obj
+                elif member == 'pop':
+                    assertion(isinstance(obj, list), 'must be applied on a list')
+                    assertion(not argvals, 'does not take any arguments')
+                    if not obj:
+                        return
+                    return obj.pop()
+                elif member == 'push':
+                    assertion(argvals, 'takes one or more arguments')
+                    obj.extend(argvals)
+                    return obj
+                elif member == 'forEach':
+                    assertion(argvals, 'takes one or more arguments')
+                    assertion(len(argvals) <= 2, 'takes at-most 2 arguments')
+                    f, this = (argvals + [''])[:2]
+                    return [f((item, idx, obj), this=this) for idx, item in enumerate(obj)]
+                elif member == 'indexOf':
+                    assertion(argvals, 'takes one or more arguments')
+                    assertion(len(argvals) <= 2, 'takes at-most 2 arguments')
+                    idx, start = (argvals + [0])[:2]
+                    try:
+                        return obj.index(idx, start)
+                    except ValueError:
+                        return -1
 
+                if isinstance(obj, list):
+                    member = int(member)
+                    nl.member = member
                 return obj[member](argvals)
 
-        for op, opfunc in _OPERATORS:
+            if remaining:
-            m = re.match(r'(?P<x>.+?)%s(?P<y>.+)' % re.escape(op), expr)
+                return self.interpret_expression(
-            if not m:
+                    self._named_object(local_vars, eval_method()) + remaining,
-                continue
+                    local_vars, allow_recursion)
-            x, abort = self.interpret_statement(
+            else:
-                m.group('x'), local_vars, allow_recursion - 1)
+                return eval_method()
-            if abort:
-                raise ExtractorError(
-                    'Premature left-side return of %s in %r' % (op, expr))
-            y, abort = self.interpret_statement(
-                m.group('y'), local_vars, allow_recursion - 1)
-            if abort:
-                raise ExtractorError(
-                    'Premature right-side return of %s in %r' % (op, expr))
-            return opfunc(x, y)
 
-        m = re.match(
+        m = re.match(r'^(?P<func>%s)\((?P<args>[a-zA-Z0-9_$,]*)\)$' % _NAME_RE, expr)
-            r'^(?P<func>%s)\((?P<args>[a-zA-Z0-9_$,]*)\)$' % _NAME_RE, expr)
         if m:
             fname = m.group('func')
             argvals = tuple([
                 int(v) if v.isdigit() else local_vars[v]
-                for v in m.group('args').split(',')]) if len(m.group('args')) > 0 else tuple()
+                for v in self._separate(m.group('args'))])
-            if fname not in self._functions:
+            if fname in local_vars:
+                return local_vars[fname](argvals)
+            elif fname not in self._functions:
                 self._functions[fname] = self.extract_function(fname)
             return self._functions[fname](argvals)
 
+        if expr:
             raise ExtractorError('Unsupported JS expression %r' % expr)
 
     def extract_object(self, objname):
@@ -233,30 +507,52 @@ class JSInterpreter(object):
 
         return obj
 
-    def extract_function(self, funcname):
+    def extract_function_code(self, funcname):
+        """ @returns argnames, code """
         func_m = re.search(
             r'''(?x)
-                (?:function\s+%s|[{;,]\s*%s\s*=\s*function|var\s+%s\s*=\s*function)\s*
+                (?:function\s+%(f_n)s|[{;,]\s*%(f_n)s\s*=\s*function|var\s+%(f_n)s\s*=\s*function)\s*
                 \((?P<args>[^)]*)\)\s*
-                \{(?P<code>[^}]+)\}''' % (
+                (?P<code>\{(?:(?!};)[^"]|"([^"]|\\")*")+\})''' % {'f_n': re.escape(funcname), },
-                re.escape(funcname), re.escape(funcname), re.escape(funcname)),
             self.code)
+        code, _ = self._separate_at_paren(func_m.group('code'), '}')  # refine the match
         if func_m is None:
             raise ExtractorError('Could not find JS function %r' % funcname)
-        argnames = func_m.group('args').split(',')
+        return func_m.group('args').split(','), code
 
-        return self.build_function(argnames, func_m.group('code'))
+    def extract_function(self, funcname):
+        return self.extract_function_from_code(*self.extract_function_code(funcname))
+
+    def extract_function_from_code(self, argnames, code, *global_stack):
+        local_vars = {}
+        while True:
+            mobj = re.search(r'function\((?P<args>[^)]*)\)\s*{', code)
+            if mobj is None:
+                break
+            start, body_start = mobj.span()
+            body, remaining = self._separate_at_paren(code[body_start - 1:], '}')
+            name = self._named_object(
+                local_vars,
+                self.extract_function_from_code(
+                    [x.strip() for x in mobj.group('args').split(',')],
+                    body, local_vars, *global_stack))
+            code = code[:start] + name + remaining
+        return self.build_function(argnames, code, local_vars, *global_stack)
 
     def call_function(self, funcname, *args):
-        f = self.extract_function(funcname)
+        return self.extract_function(funcname)(args)
-        return f(args)
 
-    def build_function(self, argnames, code):
+    def build_function(self, argnames, code, *global_stack):
-        def resf(args):
+        global_stack = list(global_stack) or [{}]
-            local_vars = dict(zip(argnames, args))
+        local_vars = global_stack.pop(0)
-            for stmt in code.split(';'):
+
-                res, abort = self.interpret_statement(stmt, local_vars)
+        def resf(args, **kwargs):
-                if abort:
+            local_vars.update(dict(zip(argnames, args)))
+            local_vars.update(kwargs)
+            var_stack = LocalNameSpace(local_vars, *global_stack)
+            for stmt in self._separate(code.replace('\n', ''), ';'):
+                ret, should_abort = self.interpret_statement(stmt, var_stack)
+                if should_abort:
                     break
-            return res
+            return ret
         return resf