[jsinterp] Fix division (#7279)

* Fixes nsig decryption for Youtube JS player `8c7583ff`

Authored by: bashonly

test/test_jsinterp.py

@@ -28,6 +28,13 @@ class TestJSInterpreter(unittest.TestCase):
     def test_calc(self):
         self._test('function f(a){return 2*a+1;}', 7, args=[3])
 
+    def test_div(self):
+        jsi = JSInterpreter('function f(a, b){return a / b;}')
+        self.assertTrue(math.isnan(jsi.call_function('f', 0, 0)))
+        self.assertTrue(math.isnan(jsi.call_function('f', JS_Undefined, 1)))
+        self.assertTrue(math.isinf(jsi.call_function('f', 2, 0)))
+        self.assertEqual(jsi.call_function('f', 0, 3), 0)
+
     def test_empty_return(self):
         self._test('function f(){return; y()}', None)
 

test/test_youtube_signature.py

@@ -150,6 +150,10 @@ _NSIG_TESTS = [
         'https://www.youtube.com/s/player/cfa9e7cb/player_ias.vflset/en_US/base.js',
         'aCi3iElgd2kq0bxVbQ', 'QX1y8jGb2IbZ0w',
     ),
+    (
+        'https://www.youtube.com/s/player/8c7583ff/player_ias.vflset/en_US/base.js',
+        '1wWCVpRR96eAmMI87L', 'KSkWAVv1ZQxC3A',
+    ),
 ]
 
 

yt_dlp/jsinterp.py

@@ -44,7 +44,7 @@ def _js_arith_op(op):
 
 
 def _js_div(a, b):
-    if JS_Undefined in (a, b) or not (a and b):
+    if JS_Undefined in (a, b) or not (a or b):
         return float('nan')
     return (a or 0) / b if b else float('inf')