The toJSON() method of the LargestContentfulPaint interface is a serializer; it returns a JSON representation of the LargestContentfulPaint object.

None.

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.

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.

• JSON