---
id: "b3dd54e4-b11b-42ea-b9d2-efa678043385"
name: "Common Pitfalls"
micro_summary: "Required reading: traps that break browser-harness commands"
status: "in_progress"
see_also: []
scope: "Traps that break browser-harness commands — document not defined, bash quote mismatches, variable collisions, stale sessions, swallowed output, and iframe context traps."
---
## Common pitfalls

1. **NameError: name 'document' is not defined** — `document` is only available inside `js()`, not in the Python wrapper.
2. **Bash syntax errors with `')`** — mismatched quotes cause bash to fail before the command even runs.
3. **Variable collisions** — `js()` accumulates state; use IIFE for multi-line code.
4. **Stale sessions** — use `ensure_real_tab()` if the tab is stale.
5. **No output from `js('...')`** — single-quoted JS sometimes swallows output; prefer double-quoted or triple-quoted.
6. **innerHTML bloat on React/Next.js** — `document.body.innerHTML` captures component definitions, compiled MDX, and scripts. Use `extract_text()` instead.
7. **iframe_target() doesn't change CDP execution context** — `iframe_target()` switches the visible frame but `js()` and `extract_text()` still execute in the parent page's CDP context. To extract iframe content, use parent-page JS: `document.querySelector("iframe")?.contentWindow?.document?.body?.innerHTML`.

---

### 2026-09-01 02:40 UTC

### 2026-08-31 — working fallback when wheel scroll dies: drive scrollTop via js()

Heuristic to find the scrollable container: `e.scrollHeight > e.clientHeight + 200 && e.clientHeight > 300` — first matching div may be a side pane rather than the target list, so verify before bumping. To scroll an element into view before `click_at_xy`, compute the target directly: `card.getBoundingClientRect().top - container.getBoundingClientRect().top + container.scrollTop`, then re-check the card's rect — a card above/below the viewport yields negative/out-of-range y and the coordinate click lands in dead space (observed: click at y=-60.125 silently did nothing; pane state unchanged). LinkedIn's classic `ul.scaffold-layout__list-container` selector was absent in the new UI; the list wrapper is a div with an obfuscated random-generated class. Structured card mining worked via `[data-job-id]` attribute collection (id + trimmed textContent per card).

---

### 2026-09-24 00:00 UTC

### 2026-09-23 — fill_input() can fail to commit on some framework-managed inputs

`fill_input()` is the helper for framework-managed inputs, but on X's bookmark search field it did not commit: the field stayed empty, then later appended instead of replacing, so a submit ran on the wrong query. Verify by reading the field's value back before pressing Enter — an appended value and a replaced one look identical in the DOM. Working fallback: native HTMLInputElement value setter plus an `input` InputEvent, then Enter.