The connectEnd property returns the timestamp immediately after the browser finishes establishing the connection to the server to retrieve the resource. The timestamp value includes the time interval to establish the transport connection, as well as other time intervals such as SSL handshake and SOCKS authentication.
The decodedBodySize property returns the size (in octets) received from the fetch (HTTP or cache) of the message body, after removing any applied content-codings. If the resource is retrieved from an application cache or local resources, it returns the size of the payload after removing any applied content-codings.
The encodedBodySize property represents the size (in octets) received from the fetch (HTTP or cache), of the payload body, before removing any applied content-codings.
The initiatorType property is a string that represents the type of resource that initiated the performance event. The value of this string is as follows:
The nextHopProtocol property is a string representing the network protocol used to fetch the resource, as identified by the ALPN Protocol ID (RFC7301).
The requestStart property returns a timestamp of the time immediately before the browser starts requesting the resource from the server, cache, or local resource. If the transport connection fails and the browser retires the request, the value returned will be the start of the retry request.
The responseEnd property returns a timestamp immediately after the browser receives the last byte of the resource or immediately before the transport connection is closed, whichever comes first.
The responseStart property returns a timestamp immediately after the browser receives the first byte of the response from the server, cache, or local resource.
The secureConnectionStart property returns a timestamp immediately before the browser starts the handshake process to secure the current connection. If a secure connection is not used, the property returns zero.
The transferSize property represents the size (in octets) of the fetched resource. The size includes the response header fields plus the response payload body (as defined by RFC7230.
If the current context is a worker, the workerStart property returns a timestamp immediately before the worker that fetches the resource is started. If the context is not a worker (i.e. a browser context), this property returns zero.
The High Resolution Time standard defines a Performance interface that supports client-side latency measurements within applications. The Performance interfaces are considered high resolution because they are accurate to a thousandth of a millisecond (subject to hardware or software constraints). The interfaces support a number of use cases including calculating frame-rates (potentially important in animations) and benchmarking (such as the time to load a resource).
The observe() method of the PerformanceObserver interface is used to specify the set of performance interface types to observe. The performance observer's callback function will be invoked when a performance entry is recorded for one of the specified types.