PerformanceEntry.startTime
The startTime
property returns the first recorded
timestamp
of the
performance entry
.
Note: This feature is available in Web Workers
The value returned by this property depends on the performance entry's
type
:
-
"
frame
" - returns thetimestamp
when the frame was started. -
"
mark
" - returns thetimestamp
when the mark was created by a call toperformance.mark()
. -
"
measure
" - returns thetimestamp
when the measure was created by a call toperformance.measure()
. -
"
navigation
" - returns thetimestamp
with a value of "0
". -
"
resource
" - returns thetimestamp
immediately before the browserstarts fetching the resource
.
This property is Read only .
Syntax
entry.startTime;
Return value
A DOMHighResTimeStamp
representing the first timestamp when the
performance entry
was created.
Note: if the performance entry has an
entryType
of "resource
" (i.e.
the entry is a PerformanceResourceTiming
object), this property returns
the PerformanceResourceTiming.fetchStart
timestamp
.
Example
The following example shows the use of the startTime
property.
function run_PerformanceEntry() {
log("PerformanceEntry support ...");
if (performance.mark === undefined) {
log("... performance.mark Not supported");
return;
}
// Create some performance entries via the mark() method
performance.mark("Begin");
do_work(50000);
performance.mark("End");
// Use getEntries() to iterate through the each entry
var p = performance.getEntries();
for (var i=0; i < p.length; i++) {
log("Entry[" + i + "]");
check_PerformanceEntry(p[i]);
}
}
function check_PerformanceEntry(obj) {
var properties = ["name", "entryType", "startTime", "duration"];
var methods = ["toJSON"];
for (var i=0; i < properties.length; i++) {
// check each property
var supported = properties[i] in obj;
if (supported)
log("..." + properties[i] + " = " + obj[properties[i]]);
else
log("..." + properties[i] + " = Not supported");
}
for (var i=0; i < methods.length; i++) {
// check each method
var supported = typeof obj[methods[i]] == "function";
if (supported) {
var js = obj[methods[i]]();
log("..." + methods[i] + "() = " + JSON.stringify(js));
} else {
log("..." + methods[i] + " = Not supported");
}
}
}
Specifications
Specification |
---|
Performance Timeline # dom-performanceentry-starttime |
Browser compatibility
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