[jsinterp] Add charcodeAt and bitwise overflow (#4706)

Authored by: elyse0

yt_dlp/jsinterp.py

@@ -18,10 +18,11 @@ from .utils import (
 
 
 def _js_bit_op(op):
+    def zeroise(x):
+        return 0 if x in (None, JS_Undefined) else x
+
     def wrapped(a, b):
-        def zeroise(x):
-            return 0 if x in (None, JS_Undefined) else x
-        return op(zeroise(a), zeroise(b))
+        return op(zeroise(a), zeroise(b)) & 0xffffffff
 
     return wrapped
 
@@ -692,6 +693,13 @@ class JSInterpreter:
                         return obj.index(idx, start)
                     except ValueError:
                         return -1
+                elif member == 'charCodeAt':
+                    assertion(isinstance(obj, str), 'must be applied on a string')
+                    assertion(len(argvals) == 1, 'takes exactly one argument')
+                    idx = argvals[0] if isinstance(argvals[0], int) else 0
+                    if idx >= len(obj):
+                        return None
+                    return ord(obj[idx])
 
                 idx = int(member) if isinstance(obj, list) else member
                 return obj[idx](argvals, allow_recursion=allow_recursion)