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Wait for a JavaScript-rendered form, then make it fillable in Python with requests

React, Vue and friends render forms after the initial HTML arrives — so a too-eager render captures a spinner where the form should be, and a pdf_forms pass finds zero controls to convert. The fix is two request parameters, no code changes on your site: "wait_until": "networkidle" holds the render until the page stops fetching, and delay adds a fixed settling pause after that.

Below is a complete, runnable Python program using requests (pip install requests). It reads your API key from the SNAPDOK_KEY environment variable — free keys take about thirty seconds and need no card.

import os
import requests

resp = requests.post(
    "https://snapdok.io/v1/render",
    headers={"Authorization": "Bearer " + os.environ["SNAPDOK_KEY"]},
    json={
        "url": "https://your-app.com/apply",
        "format": "pdf",
        "pdf_forms": True,
        "wait_until": "networkidle",
        "delay": 500,
    },
    timeout=90,
)
resp.raise_for_status()

with open("spa-form.pdf", "wb") as f:
    f.write(resp.content)
print(resp.headers.get("X-Form-Fields"), "# 0 here usually means you rendered too early")

wait_until accepts four stages, in order of patience: commit (bytes started arriving), domcontentloaded, load (the default), and networkidle (no network requests for a quiet period — the right choice for SPAs that hydrate after load). delay is an extra wait in milliseconds after that stage is reached: use a few hundred ms for forms that animate in, or that fetch their field list from an API after mount.

The feedback loop is X-Form-Fields: if it comes back 0 on a page you know has a form, the form was not in the DOM yet (or it is inside an iframe, which is never converted). Bump delay, or check the form is rendered server-side. Raise timeout (navigation cap, ms) for genuinely slow apps rather than looping retries — a failed render is never charged, but it is slower than one patient render.

Notes for requests

Three requests-specific details the sample already handles. resp.content is the binary body — resp.text would decode PDF bytes as text and corrupt them. raise_for_status() turns a JSON error response into an exception instead of letting it reach the open(..., "wb") call. And requests has no default timeout — without the explicit timeout= a hung connection blocks forever, which matters for a call that drives a real browser and legitimately takes seconds.

Response headers worth reading

HeaderMeaning
X-Form-Fields0 on a form page = rendered before the form existed.
X-Demo-Duration-MsHow long the render took (demo route).
X-CacheCached responses replay instantly.

Full parameter reference: the docs. Hard numbers on caps and timeouts: limits.

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