PerformanceLongTaskTiming: toJSON() method

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The toJSON() method of the PerformanceLongTaskTiming interface returns a JSON-serializable plain object representing the PerformanceLongTaskTiming object.

The method is automatically called by JSON.stringify() when a PerformanceLongTaskTiming object is encountered during JSON serialization.

Syntax

toJSON()

Return value

A JSON-serializable plain object containing the following properties:

Each property's value is copied as-is. When the returned object is passed to JSON.stringify(), the objects in the attribution array are further serialized using TaskAttributionTiming.toJSON().

This example obtains a PerformanceLongTaskTiming object. Calling toJSON() directly returns a plain object. Its properties have the same values as the corresponding properties of the original object.

const observer = new PerformanceObserver((list) => {
  list.getEntries().forEach((entry) => {
    const json = entry.toJSON();
    console.log(json); // A plain object
    console.log(typeof json); // "object"
    console.log(json.duration); // Same value as entry.duration
  });
});

observer.observe({ type: "longtask", buffered: true });

Serializing to a JSON string

Within the callback from the previous example, the same object can be serialized using JSON.stringify(), which calls the toJSON() method automatically.

console.log(JSON.stringify(entry));

This would log a JSON string like so (formatted for readability):

json

{
  "name": "self",
  "entryType": "longtask",
  "startTime": 183.5,
  "duration": 60,
  "navigationId": 2463,
  "attribution": [
    {
      "name": "unknown",
      "entryType": "taskattribution",
      "startTime": 0,
      "duration": 0,
      "navigationId": 2463,
      "containerType": "window",
      "containerSrc": "",
      "containerId": "",
      "containerName": ""
    }
  ]
}