Do not rely on page.goto() with waitUntil: 'load' or 'networkidle2' to prove lazy-loaded images are ready. First trigger the images by bringing their page regions into view, then wait for successful image loading and decoding before calling page.screenshot().
Why navigation waits do not guarantee images are ready
A page can finish its load event while images marked for lazy loading remain unfetched: browsers defer those images until they are near the viewport. Puppeteer defines networkidle2 as no more than two network connections for at least 500 ms; that describes network activity, not whether every desired image was requested, loaded successfully, decoded, or painted. For these browser behaviors, see MDN’s img reference and Puppeteer’s lifecycle event documentation.
Puppeteer’s screenshot guide shows navigation and Page.screenshot(), but a page that defers images needs an additional readiness step: Puppeteer screenshot guide.
Wait for images before a full-page screenshot
This example scrolls through successive page regions to trigger viewport-based lazy loading, checks for images that loaded successfully, waits for image decoding, and then captures the full page. It uses a bounded timeout and reports decode failures rather than allowing them to fail silently.
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const puppeteer = require('puppeteer');
(async () => {
const browser = await puppeteer.launch();
try {
const page = await browser.newPage();
await page.goto('https://example.com', { waitUntil: 'domcontentloaded' });
// Visit successive viewport regions so native lazy loading and
// viewport-triggered page code can request images farther down.
await page.evaluate(async () => {
const step = Math.max(1, window.innerHeight);
const height = document.documentElement.scrollHeight;
for (let y = 0; y < height; y += step) {
window.scrollTo(0, y);
await new Promise(resolve =>
requestAnimationFrame(() => requestAnimationFrame(resolve))
);
}
window.scrollTo(0, 0);
});
// A failed image can still have complete === true, so check naturalWidth.
await page.waitForFunction(
() => [...document.images].every(img => img.complete && img.naturalWidth > 0),
{ timeout: 30000 }
);
// Decode failures (for example, corrupt image data or a changed source)
// are collected so the capture can proceed with an explicit warning.
const decodeFailures = await page.evaluate(async () => {
const images = [...document.images];
const results = await Promise.all(images.map(async (img) => {
try {
await img.decode();
return null;
} catch (error) {
return { src: img.currentSrc || img.src, message: String(error) };
}
}));
return results.filter(Boolean);
});
if (decodeFailures.length) {
console.warn('Some images could not be decoded:', decodeFailures);
}
await page.screenshot({ path: 'page.png', fullPage: true });
} finally {
await browser.close();
}
})();Replace https://example.com with the page you need. The code follows Puppeteer’s documented wait-function timeout option; its default wait timeout is 30 seconds. If a failed or intentionally optional image should not stop capture, use an explicit failure policy rather than waiting forever. See Puppeteer Page.waitForFunction().
Adapt the wait to what you are capturing
Viewport-only screenshot
For a screenshot of only the visible viewport, waiting on every image in a long document can unnecessarily delay capture or fail because of an unrelated image below the fold. Scope the predicate to images in the target region, or to the images currently relevant to the viewport. A successful image check can use img.complete && img.naturalWidth > 0; then call decode() for those images when decoded image data matters to the capture.
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Full-page screenshot
fullPage: true extends the screenshot beyond the viewport, but it does not itself visit each region to trigger viewport-proximity loading. Scroll through the page first, then re-query images and run the readiness check. If scrolling or page scripts insert new content, a second pass may be needed because the image set can change after the initial scroll.
Nested scroll containers and observer-driven pages
Some sites load content when a particular element scrolls, not when the window does. The browser’s Intersection Observer API can observe intersections with the viewport or a specified root, and lazy loading is one of its use cases. If the images are inside a nested scroller, move that element through its content instead of only calling window.scrollTo().
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Check success and decoding, not just completion
HTMLImageElement.complete can be true for a broken image, so pair it with a successful-resource check such as nonzero naturalWidth. MDN documents this distinction in its complete and naturalWidth references.
img.decode() returns a promise that resolves when image data is ready to use. It may reject if the request fails, the source changes during decoding, or the data is corrupt. Decide whether those failures should stop the screenshot, be logged and skipped, or trigger a retry. See MDN’s decode() reference.
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Troubleshoot missing or delayed images
- The screenshot has blank spaces below the fold:
fullPage: truecaptures the page area but does not necessarily trigger lazy loads. Scroll through the relevant regions before checking readiness. - The wait times out: Identify which image never satisfies the predicate. It may be broken, outside the intended capture, or dynamically inserted after the check begins. Log failed URLs and decide whether to skip, retry, or fail the capture.
- The predicate passes but an image is missing: Check
naturalWidth, not onlycomplete. Then verify the image’scurrentSrc, since responsive markup can select a different resource than expected. - The image is loaded but appears unsettled: Await
decode()for the relevant images and handle rejected promises explicitly. - Scrolling the window has no effect: Find the page’s actual scroll container and move it through its regions. Observer-driven loaders may be rooted to that container.
- Images appear after the capture starts: Page scripts may add or change sources during scrolling. Re-query
document.imagesafter triggering loads and repeat the wait before taking the screenshot.
Or skip the browser setup
ScreenshotNeo offers a one-request screenshot API and an MCP server for AI agents. Its full-page capture loads lazy images. Cookie banners, popups, and chat widgets are removed before capture; bot checks, blank pages, and failed loads are never billed.
For a WebP screenshot, use cURL:
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://example.com -o shot.webpSee the ScreenshotNeo API documentation for request options. The free plan includes 1,000 screenshots per month with no card; paid plans start at $5 for 3,000. Sign up for the free plan.
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Cost and reliability considerations
Scrolling, waiting, and decoding make the capture more reliable for deferred images, but a page can keep changing or contain genuinely broken resources. Set a timeout, scope checks to the desired content, and define how to handle failures so automation cannot stall indefinitely. For dynamic pages, repeat the image query after scrolling rather than assuming the original set is complete.
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Frequently Asked Questions
Does Puppeteer’s networkidle2 wait for lazy-loaded images?
No. It indicates a period with no more than two network connections; it does not prove that offscreen lazy images were requested or decoded.
Does img.complete mean the image loaded successfully?
No. Pair it with a success check such as naturalWidth > 0.
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