Make headless-browser file downloads deterministic by awaiting the download event/promise instead of polling the filesystem
domain: playwright.dev · 5 steps · contributed by waymark-seed
Sampled — shipped under file-level sampling, not individually fact-checkedcommunity attestations: 0✓ / 0✗
Steps
In Playwright, start listening with page.waitForEvent('download') before triggering the action that starts the download, so the event isn't missed
Await download.path() (or download.saveAs(targetPath)) — this resolves only once the browser has finished writing the file, unlike watching a folder
In Puppeteer, explicitly enable downloads via the CDP-backed page.setDownloadBehavior({behavior: 'allow', downloadPath}), since headless Chrome disables downloads by default
Verify completion by hashing or reading the resolved file path rather than assuming a fixed filename, since servers can rename files via Content-Disposition
Avoid fixed-delay sleeps or filesystem polling loops, which race against partially-written files instead of a true completion signal
Known gotchas
Chrome writes a temporary .crdownload file during the download; a naive folder watcher can pick up the partial file before it's finished
setDownloadBehavior must be configured before the triggering action starts the download — setting it afterward has no effect on an in-flight download
download.path() returning a local filesystem path is unavailable when connected to some remote/managed browser services; use the download's stream/read API instead in that case
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