LargestContentfulPaint: toJSON() method
Baseline
2025
Newly available
Since December 2025, this feature works across the latest devices and browser versions. This feature might not work in older devices or browsers.
The toJSON() method of the LargestContentfulPaint interface is a serializer; it returns a JSON representation of the LargestContentfulPaint object.
Syntax
toJSON()
Parameters
None.
Return value
A JSON object that is the serialization of the LargestContentfulPaint object.
The JSON doesn't contain the element property because it is of type Element, which doesn't provide a toJSON() operation.
Examples
Using the toJSON method
In this example, calling entry.toJSON() returns a JSON representation of the LargestContentfulPaint object.
const observer = new PerformanceObserver((list) => {
list.getEntries().forEach((entry) => {
console.log(entry.toJSON());
});
});
observer.observe({ type: "largest-contentful-paint", buffered: true });
This would log a JSON object like so:
{
"name": "",
"entryType": "largest-contentful-paint",
"startTime": 468.2,
"duration": 0,
"size": 19824,
"renderTime": 468.2,
"loadTime": 0,
"id": "",
"url": ""
}
To get a JSON string, you can use JSON.stringify(entry) directly; it will call toJSON() automatically.
Specifications
| Specification |
|---|
| Largest Contentful Paint # dom-largestcontentfulpaint-tojson |