A JSON object that is the serialization of the PerformanceResourceTiming object as a map with entries from the closest inherited interface and with entries for each of the serializable attributes.
// Get a resource performance entry
var perfEntries = performance.getEntriesByType("resource");
var entry = perfEntries;
// Get the JSON and log it
var json = entry.toJSON();
var s = JSON.stringify(json);
console.log("PerformanceEntry.toJSON = " + s);