Use PDFShift’s wait_for parameter to delay conversion until a page-level function says the JavaScript-driven content is ready. The function should check the chart, font, image, or other asset your PDF actually needs—not just whether the page has loaded. If you cannot edit the source HTML, provide the readiness function with PDFShift’s javascript parameter.
Why JavaScript content can be missing from a PDF
A page’s resources can finish loading before scripts have finished rendering charts, updating data, or preparing fonts. PDF conversion that begins at that point may capture an incomplete page. PDFShift’s documentation describes wait_for as a way to let the page reach an application-specific ready state before conversion.
The key is to define readiness in terms of the output you expect. A fixed delay may work on one request and fail on another because network and rendering time vary. A readiness function can instead return true when a chart’s render promise resolves, a required element appears, or the document’s fonts finish loading.
Use a global readiness function with wait_for
Define a globally available function in the HTML being converted, then pass its name as wait_for. PDFShift calls the function repeatedly and proceeds when it returns a truthy value.
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Example: wait for a chart
Set a flag when your chart library finishes rendering, and expose a function that reports that state:
<script>
window.chartReady = false;
renderChart().then(() => {
window.chartReady = true;
});
window.isPageReady = function () {
return window.chartReady;
};
</script>Send the conversion request with wait_for set to isPageReady. Adapt the example to your chart library’s actual completion signal; do not set the flag before the chart has finished drawing.
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Example: wait for web fonts
When the PDF must use web fonts, wait for the browser’s font readiness promise and expose the result as a global function:
<script>
window.fontsReady = false;
document.fonts.ready.then(() => {
window.fontsReady = true;
});
window.isPageReady = function () {
return window.fontsReady;
};
</script>This condition addresses font loading specifically. If the document also contains asynchronous charts or other required content, include those conditions in the readiness function too.
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Inject the readiness code when you cannot edit the page
PDFShift’s javascript parameter accepts JavaScript as a string or URL. Use it to install the readiness function in the page, then pair it with wait_for. This is useful when the source page belongs to another system or cannot be changed.
The exact request syntax depends on the client library and how it encodes parameters. The essential pairing is:
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javascript: code that creates or updates a global readiness function.wait_for: the name of that function, without calling it in the parameter.
For example, injected code can set a font-ready flag after document.fonts.ready resolves and expose isPageReady to return that flag. Check PDFShift’s JavaScript documentation and your client’s request guide for the current parameter format.
Choose the readiness condition that matches the PDF
| Condition | When it fits | Trade-off |
|---|---|---|
| Component-specific signal | A chart, data widget, or other known component has a completion callback or state. | Usually the most precise check, but requires knowing how that component reports completion. |
| Page-level check | The PDF depends on several assets, such as fonts plus charts. | Covers more of the document, but every included condition must have a clear success or failure policy. |
| Fixed delay | A temporary fallback where no usable completion signal exists. | May waste time or still finish too early; it does not verify that rendering succeeded. |
Keep the function globally callable and make it return false until the required work is complete. Returning true too soon recreates the original problem; never returning true consumes the conversion’s remaining time and can lead to a timeout.
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Handle lazy-loaded images separately
Lazy-loaded images may not begin loading until the page is scrolled. PDFShift’s image guidance demonstrates scrolling down the page to trigger loading, then checking image completion before allowing conversion. A check based only on img.complete needs care: a failed image may also reach a completed state, while a check that requires every image to load successfully can remain false until timeout.
Decide what the PDF should do if an image fails. If the document can proceed without a particular image, track successful loads and errors separately and allow a bounded failure policy. If every image is essential, report the failure rather than treating it as a successful render.
Stay within PDFShift’s conversion time limit
PDFShift documents a total conversion timeout of 30 seconds for free accounts and 100 seconds for premium accounts. Loading and processing use the same total budget, so wait_for only has whatever time remains after those steps. These are vendor-published account limits, not independently measured performance figures; check PDFShift’s current documentation for changes.
Reduce avoidable work when conversion is close to the limit. PDFShift recommends reducing network requests and unnecessary scripts, and using raw HTML, inlined JavaScript and CSS, and optimized or embedded images where practical.
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- Identify the missing output. Determine whether the problem is a chart, a font, an image, or another asynchronous element. Confirm that the page’s JavaScript can run for the conversion request.
- Verify the completion signal. Check that the relevant callback or state changes only after rendering finishes—not merely after a request starts.
- Check the global function. Confirm that the name passed to
wait_forexists globally and returns a truthy value only when the required content is ready. - Inject code if needed. If you cannot edit the source page, provide the function and supporting code through
javascript. - For missing images, check lazy loading. Trigger loading by scrolling when needed, then decide how failed images should affect readiness.
- For timeouts, inspect the whole conversion budget. Loading and processing consume the same total allowance as waiting. Reduce network work or unnecessary scripts and avoid waiting on assets that are not required.
- Inspect the resulting PDF. Verify the actual chart, font, or element that prompted the change. Configuration examples cannot establish whether a particular page or conversion will succeed.
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