This specification defines an unified interface to store and retrieve performance metric data.
This specification does not cover individual performance metric interfaces.
Status of this
document
This section describes the status of this document at the time of
its publication. Other documents may supersede this document. A list of
current W3C publications and the latest revision of this technical report
can be found in the W3C technical reports
index at http://www.w3.org/TR/.
This is the W3C Proposed Recommendation of "Performance Timeline
Specification". W3C publishes a technical report as a Proposed
Recommendation to indicate that the document is a mature technical
report that has received wide review for technical soundness and
implementability and to request final endorsement from the W3C
Advisory Committee. Proposed Recommendation status is described in
section 7.1.1 of the
Process Document.
The W3C Membership and other interested parties are invited to review
the document and send comments to public-web-perf@w3.org
(archived)
with [PerformanceTimeline] at the start of the subject line through .
Advisory Committee
Representatives should consult their WBS questionnaires.
A diff document with the previous draft is also available.
By publishing this Proposed Recommendation, W3C expects that the
functionality specified in this specification will not be
affected by changes to Web IDL as that specification proceeds to
Recommendation.
Publication as a Proposed Recommendation does not imply endorsement by the
W3C Membership. This is a draft document and may be updated, replaced
or obsoleted by other documents at any time. It is inappropriate to
cite this document as other than work in progress.
Accurately measuring performance characteristics of web applications
is an important aspect of making web applications
faster. [Navigation
Timing], [Resource Timing],
and [User Timing] are examples of
specifications that define timing information related to the
navigation of the document, resources on the page, and developer
scripts, respectively.
Together these interfaces, and potentially others created in the future, define performance metrics
that describe the performance timeline of a web application. This
specification provides an unifying interface to access and retrieve these various performance metrics from the performance timeline of a
web application.
The following script shows how a developer can use the PerformanceEntry interface
to obtain timing data related to the navigation of the document, resources on the page and developer scripts.
<!doctype html>
<html>
<head>
</head>
<body onload="init()">
<img id="image0" src="http://w3c-test.org/webperf/image0.png" />
<script>
function init()
{
performance.mark("startWork"); // see [User Timing]
doWork(); // Some developer code
performance.mark("endWork");
measurePerf();
}
function measurePerf()
{
var perfEntries = performance.getEntries();
for (var i = 0; i < perfEntries.length; i++)
{
if (window.console) console.log("Name: " + perfEntries[i].name +
" Entry Type: " + perfEntries[i].entryType +
" Start Time: " + perfEntries[i].startTime +
" Duration: " + perfEntries[i].duration + "\n");
}
}
</script>
</body>
</html>
2 Conformance
requirements
All diagrams, examples, and notes in this specification are non-normative,
as are all sections explicitly marked non-normative. Everything else in this
specification is normative.
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this document
are to be interpreted as described in RFC 2119.
For readability, these words do not appear in all uppercase letters in this specification.
Requirements phrased in the imperative as part of algorithms (such as
"strip any leading space characters" or "return false and abort these steps")
are to be interpreted with the meaning of the key word ("must", "should",
"may", etc) used in introducing the algorithm.
Some conformance requirements are phrased as requirements on attributes,
methods or objects. Such requirements are to be interpreted as requirements
on user agents.
Conformance requirements phrased as algorithms or specific steps may be
implemented in any manner, so long as the end result is equivalent. (In
particular, the algorithms defined in this specification are intended to be
easy to follow, and not intended to be performant.)
The IDL fragments in this specification must be interpreted as
required for conforming IDL fragments, as described in the Web IDL
specification. [Web IDL]
3 Terminology
The construction "a Foo object", where Foo is actually an interface, is sometimes used instead of
the more accurate "an object implementing the interface Foo".
Throughout this work, all time values are measured in milliseconds since the start of
navigation of the document. For example, the start of navigation of the document
occurs at time 0. The term current time refers to the number of milliseconds
since the start of navigation of the document until the current moment in time.
This definition of time is based on the High Resolution Time specification
[High Resolution Time] and is different
from the definition of time used in the Navigation Timing specification
[Navigation Timing],
where time is measured in milliseconds since midnight of January 1, 1970 (UTC).
The startTime attribute must return a DOMHighResTimeStamp
that contains the time value of the first recorded timestamp of this performance metric.
duration attribute
The duration attribute must return a DOMHighResTimeStamp
that contains the time value of the duration of the entire event being recorded by this PerformanceEntry. Typically, this would be the
time difference between the last recorded timestamp and the first recorded timestamp of this PerformanceEntry. A performance metric may choose
to return a duration of 0, if the duration concept doesn't apply.
The getEntriesByType method returns a
PerformanceEntryList object that contains a copy of all PerformanceEntry objects, in chronological order with respect to startTime,
that have the same value for the entryType attribute of PerformanceEntry as the entryType parameter.
The getEntriesByName method returns a
PerformanceEntryList object that contains a copy of PerformanceEntry objects, in chronological order with respect to startTime,
that have the same value for the name attribute of PerformanceEntry as the name parameter
and, if specified, have the same value for the entryType attribute of PerformanceEntry as the entryType parameter.
If a vendor-specific proprietary user agent extension is needed to create experimental
PerformanceEntry objects, on getting the
entryType IDL attribute, vendors MUST return a DOMString that uses the following convention:
[vendorprefix]-[entrytype]
Where,
[vendorprefix] is a non-capitalized name that identifies the vendor,
[entrytype] is a non-capitalized name given to the type of the interface
represented by this PerformanceEntry object,
Navigation Timing, Zhiheng Wang, Editor. W3C Recommendation, World Wide Web Consortium, December 2012. This version of the Navigation Timing specification is available from http://www.w3.org/TR/2012/REC-navigation-timing-20121217/. The latest version of Navigation Timing is available at http://www.w3.org/TR/navigation-timing/.
High Resolution Time, Jatinder Mann, Editor. W3C Recommendation, World Wide Web Consortium, December 2012. This version of the High Resolution Time specification is available from http://www.w3.org/TR/2012/REC-hr-time-20121217/. The latest version of High Resolution Time is available at http://www.w3.org/TR/hr-time/.
Web IDL, Cameron McCormack, Editor. World Wide Web Consortium, April 2012. This version of the Web IDL specification is available from http://www.w3.org/TR/2012/CR-WebIDL-20120419/. The latest version of Web IDL is available at http://www.w3.org/TR/WebIDL/.
User Timing, Jatinder Mann, et al. Editors. World Wide Web Consortium, October 2013. This version of the User Timing specification is available from http://www.w3.org/TR/2013/PR-user-timing-20131031/. The latest version of User Timing is available at http://www.w3.org/TR/user-timing/.
Resource Timing, J. Mann, Z. Wang, et al. Editors. World Wide Web Consortium, May 2012. This version of the Resource Timing specification is available from http://www.w3.org/TR/2012/CR-resource-timing-20120522/. The latest version of Resource Timing is available at http://www.w3.org/TR/user-timing/.
Acknowledgements
We would like to offer our sincere thanks to all the people that we have been
in touch with regarding this draft for their reviews and feedback.