PerformanceResourceTiming.responseStart - Web APIs
the responsestart read-only property returns a timestamp immediately after the browser receives the first byte of the response from the server, cache, or local resource.
... syntax resource.responsestart; return value a domhighrestimestamp immediately after the browser receives the first byte of the response from the server.
... print_start_and_end_properties(p[i]); } } function print_start_and_end_properties(perfentry) { // print timestamps of the performanceentry *start and *end properties properties = ["connectstart", "connectend", "domainlookupstart", "domainlookupend", "fetchstart", "redirectstart", "redirectend", "requeststart", "responsestart", "responseend", "secureconnectionstart"]; for (var i=0; i < properties.length; i++) { // check each property var supported = properties[i] in perfentry; if (supported) { var value = perfentry[properties[i]]; console.log("...
..." + properties[i] + " = not supported"); } } } specifications specification status comment resource timing level 1the definition of 'responsestart' in that specification.

PerformanceTiming.responseStart - Web APIs
the legacy performancetiming.responsestart read-only property returns an unsigned long long representing the moment in time (in milliseconds since the unix epoch) when the browser received the first byte of the response from the server, cache, or local resource.
... syntax time = performancetiming.responsestart; specifications specification status comment navigation timingthe definition of 'performancetiming.responsestart' in that specification.

Navigation and resource timings - Web Performance
as displayed in the image below, the navigation process goes from navigationstart, unloadeventstart, unloadeventend, redirectstart, redirectend, fetchstart, domainlookupstart, domainlookupend, connectstart , connectend, secureconnectionstart, requeststart, responsestart, responseend, domloading, dominteractive, domcontentloadedeventstart, domcontentloadedeventend, domcomplete, loadeventstart, and loadeventend.
... responsestart when the browser received the first byte of the response, from the server from a cache, or from a local resource.
... calculating timings we can use these values to measure specific timings of interest: let dns = time.domainlookupend - time.domainlookupstart, tcp = time.connectend - time.connectstart, ssl != time.secureconnectionstart, time to first byte time to first byte is the time between the navigationstart (start of the navigation) and responsestart, (when the first byte of response data is received) available in the performancetiming api: let ttfb = time.responsestart - time.navigationstart; page load time page load time is the time between navigationstart and the start of when the load event is sent for the current document.
... request = timing.responsestart - timing.requeststart load event duration by subtracting the time stamp from immediately before the load event of the current document is fired from the time when the load event of the current document is completed, you can measure the duration of the load event.

Using the Resource Timing API - Web APIs
timing resource loading phases the following example illustrates using the resource timing properties to calculate the amount of time the following phases take: redirection (redirectstart and redirectend ), dns lookup (domainlookupstart and domainlookupend), tcp handshake (connectstart and connectend), and response (responsestart and responseend).
...secure connection time = " + t); // response time t = resources[i].responseend - resources[i].responsestart; console.log("...
... the properties which are returned as 0 by default when loading a resource from a domain other than the one of the web page itself: redirectstart, redirectend, domainlookupstart, domainlookupend, connectstart, connectend, secureconnectionstart, requeststart, and responsestart.

WebRequest.jsm
usage to import webrequest, use code like: let {webrequest} = cu.import("resource://gre/modules/webrequest.jsm", {}); the webrequest object has the following properties, each of which corresponds to a specific stage in executing a web request: onbeforerequest onbeforesendheaders onsendheaders onheadersreceived onresponsestarted oncompleted each of these objects defines two functions: addlistener(callback, filter, opt_extrainfospec) removelistener(callback) adding listeners use addlistener to add a listener to a particular event.
... onresponsestarted triggered once the browser has started to receive the response body.

Index - Web APIs
3043 performanceresourcetiming.responsestart api, property, reference, web performance the responsestart read-only property returns a timestamp immediately after the browser receives the first byte of the response from the server, cache, or local resource.
... 3072 performancetiming.responsestart api, backwards compatibility, deprecated, navigation timing, performancetiming, property, read-only, reference, legacy the legacy performancetiming.responsestart read-only property returns an unsigned long long representing the moment in time (in milliseconds since the unix epoch) when the browser received the first byte of the response from the server, cache, or local resource.

Resource Timing API - Web APIs
the last three timestamps are, in order: requeststart - the timestamp before the browser starts requesting the resource from the server; responsestart - the timestamp after the browser receives the first byte of the response from the server; and responseend - the timestamp after the browser receives the last byte of the resource.
... the properties which are returned as 0 by default when loading a resource from a domain other than the one of the web page itself: redirectstart, redirectend, domainlookupstart, domainlookupend, connectstart, connectend, secureconnectionstart, requeststart, and responsestart.

Time to first byte - MDN Web Docs Glossary: Definitions of Web-related terms
ttfb is the time it takes between the start of the request and the start of the response, in milliseconds: ttfb = responsestart - requeststart see also: a typical http session performanceresourcetiming performancetiming ...

Web Console remoting - Firefox Developer Tools
headers", "headers": 10, "headerssize": 425 }, { "from": "conn0.netevent14", "type": "networkeventupdate", "updatetype": "requestcookies", "cookies": 0 }, { "from": "conn0.netevent14", "type": "networkeventupdate", "updatetype": "requestpostdata", "datasize": 1024, "discardrequestbody": false }, { "from": "conn0.netevent14", "type": "networkeventupdate", "updatetype": "responsestart", "response": { "httpversion": "http/1.1", "status": "304", "statustext": "not modified", "headerssize": 194, "discardresponsebody": true } }, { "from": "conn0.netevent14", "type": "networkeventupdate", "updatetype": "eventtimings", "totaltime": 1 }, { "from": "conn0.netevent14", "type": "networkeventupdate", "updatetype": "responseheaders", "headers": 6, ...

PerformanceNavigationTiming - Web APIs
performancenavigationtiming.responsestart read only a domhighrestimestamp representing the time immediately after the user agent's http parser receives the first byte of the response from relevant application caches, or from local resources or from the server.

PerformanceResourceTiming.connectEnd - Web APIs
ength; i++) { print_start_and_end_properties(p[i]); } } function print_start_and_end_properties(perfentry) { // print timestamps of the *start and *end properties properties = ["connectstart", "connectend", "domainlookupstart", "domainlookupend", "fetchstart", "redirectstart", "redirectend", "requeststart", "responsestart", "responseend", "secureconnectionstart"]; for (var i=0; i < properties.length; i++) { // check each property var supported = properties[i] in perfentry; if (supported) { var value = perfentry[properties[i]]; console.log("...

PerformanceResourceTiming.connectStart - Web APIs
print_start_and_end_properties(p[i]); } } function print_start_and_end_properties(perfentry) { // print timestamps of the performanceentry *start and *end properties properties = ["connectstart", "connectend", "domainlookupstart", "domainlookupend", "fetchstart", "redirectstart", "redirectend", "requeststart", "responsestart", "responseend", "secureconnectionstart"]; for (var i=0; i < properties.length; i++) { // check each property var supported = properties[i] in perfentry; if (supported) { var value = perfentry[properties[i]]; console.log("...

PerformanceResourceTiming.domainLookupEnd - Web APIs
ength; i++) { print_start_and_end_properties(p[i]); } } function print_start_and_end_properties(perfentry) { // print timestamps of the *start and *end properties properties = ["connectstart", "connectend", "domainlookupstart", "domainlookupend", "fetchstart", "redirectstart", "redirectend", "requeststart", "responsestart", "responseend", "secureconnectionstart"]; for (var i=0; i < properties.length; i++) { // check each property var supported = properties[i] in perfentry; if (supported) { var value = perfentry[properties[i]]; console.log("...

PerformanceResourceTiming.domainLookupStart - Web APIs
print_start_and_end_properties(p[i]); } } function print_start_and_end_properties(perfentry) { // print timestamps of the performanceentry *start and *end properties properties = ["connectstart", "connectend", "domainlookupstart", "domainlookupend", "fetchstart", "redirectstart", "redirectend", "requeststart", "responsestart", "responseend", "secureconnectionstart"]; for (var i=0; i < properties.length; i++) { // check each property var supported = properties[i] in perfentry; if (supported) { var value = perfentry[properties[i]]; console.log("...

PerformanceResourceTiming.fetchStart - Web APIs
print_start_and_end_properties(p[i]); } } function print_start_and_end_properties(perfentry) { // print timestamps of the performanceentry *start and *end properties properties = ["connectstart", "connectend", "domainlookupstart", "domainlookupend", "fetchstart", "redirectstart", "redirectend", "requeststart", "responsestart", "responseend", "secureconnectionstart"]; for (var i=0; i < properties.length; i++) { // check each property var supported = properties[i] in perfentry; if (supported) { var value = perfentry[properties[i]]; console.log("...