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The correct callback depends on what you mean by “image.” For an interactive Plotly chart, chain code to the promise returned by Plotly.newPlot(). To run code after every plotting pass, listen for plotly_afterplot. For a static export, await Plotly.toImage(); that promise means Plotly has generated the image data URL, not necessarily that the browser has finished decoding an <img>.
Choose the completion signal first
| What must be complete? | Use | Meaning |
|---|---|---|
| Initial interactive chart render | Plotly.newPlot(...).then(...) |
The initial plot call has completed. |
| Every chart plotting pass | plotly_afterplot |
The graph has been plotted again, including after updates such as restyle or relayout. |
| Plotly-generated static image | Plotly.toImage(...) |
Plotly has produced an image data URL. |
These are different lifecycle points. A chart rendered into a graph div is not the same thing as an exported image, and an exported data URL is not the same thing as the browser decoding an <img>. Plotly’s official documentation covers the first two signals and the export promise: event handlers, the function reference, and static image export.
Run code once after the initial Plotly render
Use the promise returned by Plotly.newPlot when your code should run once after the initial chart has been plotted.
const data = [
{
x: ['Jan', 'Feb', 'Mar'],
y: [12, 19, 15],
type: 'bar'
}
];
const layout = { title: 'Quarterly example' };
Plotly.newPlot('myDiv', data, layout)
.then((gd) => {
// The initial interactive chart render has completed.
runMyCode(gd);
})
.catch((error) => {
console.error('Plotly failed to render:', error);
});
function runMyCode(graphDiv) {
graphDiv.classList.add('chart-ready');
console.log('Ready:', graphDiv);
}The resolved value is the graph div (gd). Keeping that reference is useful when the same page contains several charts. A promise callback also lets you handle a rendering failure instead of silently running code too early.
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Use a graph-div reference
You can pass the DOM element rather than its ID. This avoids looking it up again in the callback:
const gd = document.getElementById('myDiv');
Plotly.newPlot(gd, data, layout).then(() => {
gd.setAttribute('aria-busy', 'false');
});Set any loading state before calling newPlot, then clear it in the promise handler. Do not substitute an arbitrary setTimeout; a timer is only a guess and can fire before a slow plot has completed.
Run code after every plotting pass
If your handler must run again after Plotly.react, Plotly.restyle, Plotly.relayout, or another operation causes the chart to be plotted, attach a plotly_afterplot listener to the graph div.
const gd = document.getElementById('myDiv');
gd.on('plotly_afterplot', () => {
runAfterEveryPlot(gd);
});
// Attach the listener before this call so it also catches the initial pass.
Plotly.newPlot(gd, data, layout);
function runAfterEveryPlot(graphDiv) {
console.log('A plotting pass completed');
document.querySelector('#status').textContent = 'Chart ready';
}Plotly documents plotly_afterplot as an event triggered each time a chart is plotted. Because it can recur, make the handler idempotent: update existing UI, rather than appending duplicate controls or registering duplicate listeners on every event.
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Prevent duplicate work
let lastRevision = 0;
gd.on('plotly_afterplot', () => {
const revision = gd.layout?.datarevision;
if (revision === lastRevision) return;
lastRevision = revision;
updateOverlay(gd);
});Only add a guard when your application has a reliable revision value. In many cases, simply making updateOverlay replace its output is safer than trying to infer whether a plot changed.
Wait for a static image generated by Plotly
For a PNG, JPEG, WebP, or other export created from a chart, first await the plot and then await Plotly.toImage. The export promise resolves with a data URL.
async function createExport() {
const gd = await Plotly.newPlot('myDiv', data, layout);
const imageUrl = await Plotly.toImage(gd, {
format: 'png',
width: 800,
height: 600
});
const img = document.getElementById('exportedImage');
img.src = imageUrl;
// Plotly has generated the URL and it has been assigned to the image.
afterExportGenerated(imageUrl);
}
createExport().catch((error) => {
console.error('Could not create export:', error);
});This follows Plotly’s documented export flow. The toImage promise tells you that Plotly produced the image data URL. The official pages do not define that promise as a guarantee that the browser has completed a later image-display or decode milestone.
If you need the browser’s image decode milestone
After assigning src, use the browser’s image API when your next operation requires decoded pixels. img.decode() returns a promise in browsers that support it; an onload handler is the broadly compatible fallback.
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async function putExportInPage() {
const gd = await Plotly.newPlot('myDiv', data, layout);
const imageUrl = await Plotly.toImage(gd, { format: 'png', width: 800, height: 600 });
const img = document.getElementById('exportedImage');
img.src = imageUrl;
if (img.decode) {
await img.decode();
} else if (!img.complete) {
await new Promise((resolve, reject) => {
img.onload = resolve;
img.onerror = reject;
});
}
// The browser has completed the decode step (where supported).
afterBrowserDecode(img);
}This browser-level step is separate from Plotly’s documented export lifecycle. If the image is already cached, complete may be true immediately; check the element’s state before installing a listener.
Complete examples for common application patterns
Disable a loading indicator
const gd = document.getElementById('myDiv');
const spinner = document.getElementById('spinner');
gd.on('plotly_afterplot', () => {
spinner.hidden = true;
});
Plotly.newPlot(gd, data, layout).catch(() => {
spinner.textContent = 'Chart could not be loaded';
});Run once, then react to updates
const gd = document.getElementById('myDiv');
let initialized = false;
gd.on('plotly_afterplot', () => {
if (!initialized) {
initialized = true;
initializeChartControls(gd);
}
refreshChartDependentUi(gd);
});
await Plotly.newPlot(gd, data, layout);
await Plotly.restyle(gd, { y: [[20, 14, 18]] });The listener catches both the initial pass and the later restyle. Use Plotly.newPlot(...).then(...) instead when controls must be initialized only once and do not need to observe future plotting.
Failure modes and fixes
The callback never runs
- Check that the Plotly script loaded before your code and that
Plotlyexists. - Verify that
myDivis present and is the graph div, not a wrapper around it. - Attach
plotly_afterplotbeforePlotly.newPlot; attaching afterward can miss the initial event. - Always add a
.catchto the promise so a rendering error is visible.
The handler runs more than once
That is expected for plotly_afterplot. It is an every-pass event, including update-driven plotting. Make the handler idempotent, use a one-time initialization flag, or switch to the newPlot promise for initial-only work.
The image is blank or has the wrong size
- Provide explicit
widthandheighttoPlotly.toImagewhen the layout’s responsive size is not established. - Await
newPlotbefore callingtoImage. - Inspect the rejected promise; export can fail if the chart or its dependencies did not render correctly.
Code runs before an image appears
Decide which milestone you need. The toImage promise covers export generation. Assign its URL to img.src, then await img.decode() or handle onload if you need browser decoding. Neither a timer nor the plot event alone proves that a separate <img> element has decoded.
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Updates trigger expensive work repeatedly
Keep the event handler small, debounce application work if updates arrive in bursts, and avoid calling another plotting method from the handler unless you intentionally need a second pass. A handler that mutates the chart on every plotly_afterplot can create a feedback loop.
Performance and reliability considerations
- Prefer promise chaining for a single known operation; it avoids an always-on listener.
- Prefer
plotly_afterplotwhen several code paths can replot the same graph and all must notify the UI. - Register listeners once, especially in component frameworks where mounting can happen repeatedly. Remove them with your framework’s cleanup mechanism when the graph is destroyed.
- Do not treat a successful callback as proof that remote data requests, fonts, or unrelated page images have finished. It signals Plotly’s documented plot or export milestone.
- Handle rejection and event-handler exceptions separately so a UI update failure does not hide the original rendering error.
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Equivalent Python request
import requests
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params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"},
timeout=90,
)
r.raise_for_status()
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const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);
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Which approach should you use?
- Use
Plotly.newPlot(...).then(...)for one action after the initial interactive render. - Use
plotly_afterplotfor an action after every plotting pass. - Use
Plotly.toImage(...)for the completion of Plotly’s static export generation. - Use
img.decode()oronloadafter assigning the export URL when browser image decoding is the actual requirement.
Frequently Asked Questions
Does Plotly have an image-load event for a chart in a div?
For an interactive chart, use the promise from Plotly.newPlot or the plotly_afterplot event; an HTML image-load event applies to an img element, not the graph div.
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Can I use plotly_afterplot only for the first render?
It can fire on later plotting passes too. Add a one-time flag in the handler or use the newPlot promise for initial-only code.
Does Plotly.toImage wait for the browser to display the image?
No documented guarantee covers that later display milestone. It resolves when Plotly has generated the image data URL; await img.decode or use onload after assigning src if decoding matters.
The Bottom Line
Match the callback to the milestone: newPlot for the initial chart, plotly_afterplot for every plot, and toImage for export generation.
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