---
id: "5f07c543-03d1-4221-b190-de5a8a8c5d66"
name: "Probing Strategy"
micro_summary: "Step-by-step DOM inspection pattern: single-line JS checks → IIFE extraction → data-* attributes → text vs HTML → JSON.stringify for structured data"
status: "in_progress"
see_also: []
scope: "How to run browser-harness -c, js() state accumulation, and the probing strategy"
---
## Running browser-harness -c

The `-c` argument runs **Python**, not JavaScript. This is the #1 source of errors.

```bash
browser-harness -c '
wait_for_load()
wait(1)
result = js("document.querySelector(\".item\").textContent")
print(result)
'
```

**Quote nesting:** outer `'` for bash, inner `"` for JS strings.

## js() accumulates state

`js()` evaluates in the **same global scope** across calls. Variables declared in one call persist.

- **Single-line expressions:** fine as-is — no state to clash.
  ```python
  js("document.querySelectorAll(\".item\").length")
  ```
- **Multi-line code:** wrap in an **IIFE** to isolate scope.
  ```python
  js("""(function() {
    const items = document.querySelectorAll(".planner-item");
    const results = [];
    for (let i = 0; i < 5; i++) {
      const el = items[i];
      results.push({ text: el.textContent.substring(0, 100) });
    }
    return JSON.stringify(results);
  })()""")
  ```

**Without the IIFE**, `const items` fails on the second call with `SyntaxError: Identifier 'items' has already been declared`.

## Probing strategy
1. **Single-line JS** for quick checks: `js("document.querySelector('.item').innerHTML")`
2. **IIFE-wrapped multi-line** for structured extraction.
3. **Inspect `data-*` attributes** for structured data (`data-testid`, `data-cid`, etc.).
4. **Use `innerText`** for human-readable text, **`innerHTML`** for DOM structure.
5. **`JSON.stringify()`** for returning structured data from JS to Python.

---

### 2026-08-15 01:34 UTC

## 2026-08-15 — v0.1.8 correction

The `-c` section above is historical. Send the same Python wrapper through stdin with a heredoc. This removes the shell's nested Python argument quoting layer; JavaScript still belongs inside `js(...)`, and IIFEs remain useful for multi-line JavaScript state isolation.