Use an HTML file input and ElementHandle.uploadFile() to upload files. For a native picker, arm page.waitForFileChooser() before clicking and then accept the file. Downloads need more care: create a browser context with an explicit writable downloadPath, then prove completion with a bounded filesystem or protocol check and an application-level assertion. Puppeteer’s maintained files guide currently says it has no universal programmatic download API, so download configuration alone is not completion detection.
What you need before handling files
- Install a current Puppeteer release (the
puppeteerpackage downloads a compatible Chrome by default) or usepuppeteer-corewhen your team manages the browser binary. - Use absolute paths on the machine running Puppeteer. A path on your laptop is not available to a remote CI worker or container unless you mount or copy it there.
- Give each job its own empty, writable download directory. This prevents an old file or another test from being mistaken for the current result.
API details can change between Puppeteer versions and between Chrome DevTools Protocol and WebDriver BiDi. Check the installed version’s references for file handling, DownloadBehavior, and the Page API.
Upload a file through an HTML input
Basic upload
Most upload controls contain an <input type="file">, even when a styled button hides it. Locate that input and pass one or more absolute paths:
const fileElement = await page.waitForSelector('input[type=file]');
await fileElement.uploadFile('/absolute/path/to/report.pdf');For a multiple-file input, pass additional paths:
await fileElement.uploadFile(
'/absolute/path/to/report.pdf',
'/absolute/path/to/data.csv'
);uploadFile changes the browser’s selected files; it does not submit the form or prove that the server received the bytes. Use the application’s submit control and wait for the response, navigation, or a visible success state.
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Submit and verify the server response
const [response] = await Promise.all([
page.waitForResponse(r => r.url().includes('/upload') && r.ok()),
page.locator('button[type=submit]').click(),
]);
if (!response.ok()) throw new Error(`Upload failed: ${response.status()}`);
await page.locator('[data-testid="upload-success"]').wait();Use the site’s real endpoint or success selector. A 200 response may still represent an application-level error, so inspect the response body when the API defines a success field.
Handle a button that opens the native file chooser
When JavaScript opens a system picker instead of exposing a usable input, register the chooser wait before the action. Waiting afterward can miss the event.
const [chooser] = await Promise.all([
page.waitForFileChooser({timeout: 5000}),
page.locator('#choose-file').click(),
]);
await chooser.accept(['/absolute/path/to/report.pdf']);For multiple files, the underlying input must support multiple. Do not rewrite the page’s attributes merely to bypass validation; follow the application’s intended flow and then verify its upload result.
Configure a controlled browser download
Create an isolated context and destination
Set the context download policy and destination when the browser supports it. The destination must be absolute and writable; downloadPath is required with allow or allowAndName.
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import fs from 'node:fs/promises';
const downloadPath = '/absolute/path/to/job-directory';
await fs.mkdir(downloadPath, {recursive: true});
for (const name of await fs.readdir(downloadPath)) {
await fs.rm(`${downloadPath}/${name}`, {force: true});
}
const browser = await puppeteer.launch();
const context = await browser.createBrowserContext({
downloadBehavior: {
policy: 'allow',
downloadPath,
},
});
const page = await context.newPage();Treat that directory as owned by one job. If you use allowAndName, files are named with a download GUID; the DownloadBehavior reference documents a WebDriver BiDi limitation for that policy. Do not infer a final user-facing filename from a GUID without your own mapping.
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Trigger the download without a race
Arm the wait for the event that proves the click’s asynchronous result before clicking:
await Promise.all([
page.waitForNavigation({waitUntil: 'domcontentloaded'}),
page.locator('a[data-download]').click(),
]);If the click does not navigate, wait for the application response instead:
const [downloadResponse] = await Promise.all([
page.waitForResponse(r => r.url().includes('/export') && r.ok()),
page.locator('#export').click(),
]);A response or navigation confirms the trigger, not necessarily that all bytes have been flushed to disk. Continue with completion checks.
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Know when the download is finished
Puppeteer’s maintained files guide explicitly states: “Currently, Puppeteer does not offer a way to handle file downloads in a programmatic way.” There is no universal, supported page.on('download') API that replaces your own completion logic. Use one or more of these signals.
Bounded directory polling
Poll a clean job directory until the expected file exists, temporary .crdownload files disappear, and the size remains unchanged for consecutive checks. Always enforce a deadline.
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import fs from 'node:fs/promises';
async function waitForStableFile(dir, expectedName, {
timeoutMs = 60_000,
intervalMs = 500,
stableChecks = 3,
} = {}) {
const deadline = Date.now() + timeoutMs;
let previousSize = -1;
let stable = 0;
while (Date.now() < deadline) {
const names = await fs.readdir(dir);
if (names.some(n => n.endsWith('.crdownload'))) {
stable = 0;
} else if (names.includes(expectedName)) {
const stat = await fs.stat(`${dir}/${expectedName}`);
if (stat.size > 0 && stat.size === previousSize) stable++;
else stable = 0;
previousSize = stat.size;
if (stable >= stableChecks) return `${dir}/${expectedName}`;
}
await new Promise(resolve => setTimeout(resolve, intervalMs));
}
throw new Error(`Download did not complete within ${timeoutMs} ms`);
}Stable size is only a heuristic. Validate the expected byte count, checksum, archive contents, or a downstream parser before accepting the artifact. Reject files that pre-date the job or exceed your size limit.
Use protocol or application signals when available
Some Chrome protocol integrations expose download-begun and download-completed notifications. If you use them, still correlate the event with the current job and verify the final path and integrity. An application-generated “export ready” state can be stronger than a generic browser event.
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If the file URL is stable and your authorization permits it, an HTTP client avoids browser download-policy differences. Preserve only the required origin-scoped cookies or bearer token, check status and content type, stream with a maximum size, and write to the job directory atomically.
const response = await fetch(fileUrl, {
headers: {Authorization: `Bearer ${process.env.DOWNLOAD_TOKEN}`},
});
if (!response.ok) throw new Error(`HTTP ${response.status}`);
const contentType = response.headers.get('content-type') || '';
if (!contentType.includes('application/pdf')) throw new Error('Unexpected content type');
const bytes = Buffer.from(await response.arrayBuffer());
if (bytes.length === 0 || bytes.length > 100 * 1024 * 1024) throw new Error('Invalid size');
await fs.writeFile('/absolute/path/to/job-directory/report.pdf', bytes);
Keep browser interaction when authentication, navigation, a CSRF token, or a required user gesture is part of the behavior you are testing.
Race-free synchronization patterns
- Put the wait and the action in the same
Promise.all. This applies to file choosers, navigation, and response waits. - Use selectors and URL predicates specific to the operation; a generic network-idle wait can resolve before a queued export starts.
- Give every wait a finite timeout and include the URL, selector, and job identifier in the error.
- Close the page, context, and browser in a
finallyblock, while retaining a failed job directory long enough for diagnosis.
Troubleshooting uploads and downloads
“No element found” or upload does nothing
The control may be inside an iframe, shadow root, or rendered after an interaction. Select the correct frame, wait for the input’s visibility or attachment, and confirm that the path exists and is readable by the Puppeteer process.
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The chooser timeout expires
The button may not open a native chooser, or the wait was registered after the click. Prefer the actual file input when available; otherwise place waitForFileChooser before the click and verify the selector targets the active control.
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The server says no file was received
Selection alone is not submission. Click the site’s submit button, wait for its upload request, and inspect the response body and success indicator. Check field names and required metadata expected by the server.
The download directory stays empty
Confirm the context—not just another browser context—was created with policy: 'allow' and an absolute writable path. Check that the click was not blocked by a popup, consent screen, authentication redirect, or bot check.
A stale or partial file is accepted
Start with an empty per-job directory, reject .crdownload files, require a bounded deadline, and verify size, checksum, magic bytes, or successful parsing. Never treat a nonzero size by itself as proof of completion.
Works in Chrome but not Firefox or BiDi
Download behavior and notification support differ by browser and protocol. Re-check the version-specific API reference, run a small compatibility test in the target browser, and fall back to an authorized HTTP request where appropriate.
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Performance, reliability, and security
- Reuse a browser process when safe, but isolate cookies, permissions, and download directories per job with separate contexts.
- Stream or impose size limits for large files; avoid holding untrusted multi-gigabyte responses in memory.
- Sanitize server-provided filenames and prevent path traversal. Write to a temporary name, validate it, then rename atomically.
- Keep credentials in environment variables or a secret manager. Do not log cookies, authorization headers, or uploaded file contents.
- Clean up old artifacts according to a retention policy, while preserving failed jobs needed for debugging.
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Frequently Asked Questions
Where are Puppeteer downloads saved by default?
Do not rely on an implicit location. Configure a writable absolute downloadPath on the browser context and treat that directory as the job’s destination.
Can I upload a file by setting the input value with JavaScript?
No. Use Puppeteer’s uploadFile on the real file input, or accept the file through a chooser returned by waitForFileChooser; then submit and verify the application result.
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No. Correlate it with the current job and validate the final filename, size or checksum, and—when possible—the file format or application-level result.
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