fix: propagate JavaScript evaluation errors

Author: Lhy099

helpers.py

@@ -226,6 +226,11 @@ def wait_for_selector(selector, timeout=10.0, visible=False, interval=0.2):
 """
     return bool(wait_for_js(expression, timeout=timeout, interval=interval))
 
+def _js_exception_text(r):
+    d = r.get("exceptionDetails") or {}
+    e = d.get("exception") or {}
+    return "\n".join(str(x) for x in (d.get("text"), e.get("description"), e.get("value")) if x)
+
 def js(expression, target_id=None):
     """Run JS in the attached tab (default) or inside an iframe target (via iframe_target()).
 
@@ -236,6 +241,8 @@ def js(expression, target_id=None):
     if "return " in expression:
         expression = f"(function(){{{expression}}})()"
     r = cdp("Runtime.evaluate", session_id=sid, expression=expression, returnByValue=True, awaitPromise=True)
+    if "exceptionDetails" in r:
+        raise RuntimeError(f"JavaScript evaluation failed: {_js_exception_text(r) or 'unknown error'}")
     return r.get("result", {}).get("value")
 
 def page_outline(limit=80):

test_js.py

@@ -1,3 +1,4 @@
+import pytest
 from unittest.mock import patch
 import helpers
 
@@ -28,6 +29,20 @@ def test_return_statement_gets_wrapped():
     assert _evaluated_expression(captured) == "(function(){const x = 1; return x})()"
 
 
+def test_js_raises_on_runtime_exception():
+    def fake_cdp(method, **kwargs):
+        return {
+            "exceptionDetails": {
+                "text": "Uncaught ReferenceError",
+                "exception": {"description": "ReferenceError: missing is not defined"},
+            }
+        }
+
+    with patch("helpers.cdp", side_effect=fake_cdp):
+        with pytest.raises(RuntimeError, match="missing is not defined"):
+            helpers.js("missing.value")
+
+
 def test_wait_for_js_returns_first_truthy_value():
     with patch("helpers.js", side_effect=[False, None, {"ready": True}]), \
          patch("helpers.time.sleep") as sleep:
@@ -36,6 +51,15 @@ def test_wait_for_js_returns_first_truthy_value():
     assert sleep.call_count == 2
 
 
+def test_wait_for_js_propagates_js_errors():
+    with patch("helpers.js", side_effect=RuntimeError("JavaScript evaluation failed")), \
+         patch("helpers.time.sleep") as sleep:
+        with pytest.raises(RuntimeError, match="JavaScript evaluation failed"):
+            helpers.wait_for_js("missing.value", timeout=1, interval=0.01)
+
+    sleep.assert_not_called()
+
+
 def test_wait_for_selector_uses_visible_predicate():
     with patch("helpers.wait_for_js", return_value=True) as wait:
         assert helpers.wait_for_selector("button[aria-label='Save']", timeout=3, visible=True)