files/en-us/web/api/performanceservertiming/tojson/index.md
{{APIRef("Performance API")}}{{AvailableInWorkers}}
The toJSON() method of the {{domxref("PerformanceServerTiming")}} interface is a {{Glossary("Serialization","serializer")}}; it returns a JSON representation of the {{domxref("PerformanceServerTiming")}} object.
toJSON()
None.
A {{jsxref("JSON")}} object that is the serialization of the {{domxref("PerformanceServerTiming")}} object.
Server timing metrics require the server to send the {{HTTPHeader("Server-Timing")}} header. For example:
Server-Timing: cache;desc="Cache Read";dur=23.2
The serverTiming entries can live on navigation and resource entries.
Example using a {{domxref("PerformanceObserver")}}, which notifies of new navigation and resource performance entries as they are recorded in the browser's performance timeline. Use the buffered option to access entries from before the observer creation.
const observer = new PerformanceObserver((list) => {
list.getEntries().forEach((entry) => {
entry.serverTiming.forEach((serverEntry) => {
console.log(serverEntry.toJSON());
});
});
});
["navigation", "resource"].forEach((type) =>
observer.observe({ type, buffered: true }),
);
This would log a JSON object like so:
{
"name": "cache",
"duration": 23.2,
"description": "Cache Read"
}
To get a JSON string, you can use JSON.stringify(serverEntry) directly; it will call toJSON() automatically.
{{Specifications}}
{{Compat}}