[jsinterp] Support `if` statements

Closes #6131

test/test_jsinterp.py

@@ -155,6 +155,38 @@ class TestJSInterpreter(unittest.TestCase):
         self.assertEqual(jsi.call_function('z'), 5)
         self.assertEqual(jsi.call_function('y'), 2)
 
+    def test_if(self):
+        jsi = JSInterpreter('''
+        function x() {
+            let a = 9;
+            if (0==0) {a++}
+            return a
+        }''')
+        self.assertEqual(jsi.call_function('x'), 10)
+
+        jsi = JSInterpreter('''
+        function x() {
+            if (0==0) {return 10}
+        }''')
+        self.assertEqual(jsi.call_function('x'), 10)
+
+        jsi = JSInterpreter('''
+        function x() {
+            if (0!=0) {return 1}
+            else {return 10}
+        }''')
+        self.assertEqual(jsi.call_function('x'), 10)
+
+        """  # Unsupported
+        jsi = JSInterpreter('''
+        function x() {
+            if (0!=0) {return 1}
+            else if (1==0) {return 2}
+            else {return 10}
+        }''')
+        self.assertEqual(jsi.call_function('x'), 10)
+        """
+
     def test_for_loop(self):
         jsi = JSInterpreter('''
         function x() { a=0; for (i=0; i-10; i++) {a++} return a }

test/test_youtube_signature.py

@@ -134,6 +134,10 @@ _NSIG_TESTS = [
         'https://www.youtube.com/s/player/7a062b77/player_ias.vflset/en_US/base.js',
         'NRcE3y3mVtm_cV-W', 'VbsCYUATvqlt5w',
     ),
+    (
+        'https://www.youtube.com/s/player/dac945fd/player_ias.vflset/en_US/base.js',
+        'o8BkRxXhuYsBCWi6RplPdP', '3Lx32v_hmzTm6A',
+    ),
 ]
 
 

yt_dlp/jsinterp.py

@@ -403,10 +403,25 @@ class JSInterpreter:
 
         m = re.match(r'''(?x)
                 (?P<try>try)\s*\{|
+                (?P<if>if)\s*\(|
                 (?P<switch>switch)\s*\(|
                 (?P<for>for)\s*\(
                 ''', expr)
         md = m.groupdict() if m else {}
+        if md.get('if'):
+            cndn, expr = self._separate_at_paren(expr[m.end() - 1:])
+            if_expr, expr = self._separate_at_paren(expr.lstrip())
+            # TODO: "else if" is not handled
+            else_expr = None
+            m = re.match(r'else\s*{', expr)
+            if m:
+                else_expr, expr = self._separate_at_paren(expr[m.end() - 1:])
+            cndn = _js_ternary(self.interpret_expression(cndn, local_vars, allow_recursion))
+            ret, should_abort = self.interpret_statement(
+                if_expr if cndn else else_expr, local_vars, allow_recursion)
+            if should_abort:
+                return ret, True
+
         if md.get('try'):
             try_expr, expr = self._separate_at_paren(expr[m.end() - 1:])
             err = None