The startTime
property returns the first recorded timestamp
of the performance entry
.
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 PerformanceEntry.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 | Status | Comment |
---|---|---|
Performance Timeline Time Level 2 The definition of 'startTime' in that specification. |
Editor's Draft | |
Performance Timeline The definition of 'startTime' in that specification. |
Recommendation | Initial definition. |
Browser compatibility
Feature | Chrome | Edge | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
---|---|---|---|---|---|---|
Basic support. | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | No support |
Feature | Android | Edge | Firefox Mobile (Gecko) | Firefox OS | IE Phone | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|---|
Basic support. | (Yes) | (Yes) | 25.0 (25.0) | 1.2 (25.0) | 10.0 | (Yes) | No support |