Performance Timeline

Abstract

This specification defines an interface for web applications to access timing information related to navigation and elements.

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 a First Public Working Draft of "Performance Timeline".

Please send comments to public-web-perf@w3.org (archived) with [PerformanceTimeline] at the start of the subject line.

This document is produced by the Web Performance Working Group. The Web Performance Working Group is part of the Rich Web Clients Activity in the W3C Interaction Domain.

You can find the latest Editor's Draft of this document in the W3C's Mercurial repository, which is updated on a regular basis.

Publication as a Working Draft 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.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Implementers should be aware that this document is not stable. Implementers who are not taking part in the discussions are likely to find the specification changing out from under them in incompatible ways. Vendors interested in implementing this document before it eventually reaches the Candidate Recommendation stage should join the aforementioned mailing lists and take part in the discussions.

Table of Contents

1. 1 Introduction
2. 2 Conformance requirements
3. 3 Terminology
4. 4 Performance Timeline
   1. 4.1 The Performance Timeline
   2. 4.2 The PerformanceEntry interface
   3. 4.3 The PerformanceEntryList interface
   4. 4.4 The window.performance attribute
   5. 4.5 The PerformanceTiming interface
5. 5 References
6. Acknowledgements

1 Introduction

This section is non-normative.

This specification introduces a unified interface to store and retrieve performance metric data. This specification does not cover individual performance metric interfaces.

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".

The term DOM is used to refer to the API set made available to scripts in Web applications, and does not necessarily imply the existence of an actual Document object or of any other Node objects as defined in the DOM Core specifications.

A DOM attribute is said to be getting when its value is being retrieved (such as by author script), and is said to be setting when a new value is assigned to it.

The term "JavaScript" is used to refer to ECMA-262, rather than the official term ECMAScript, since the term JavaScript is more widely known.

Throughout this work, time is measured in milliseconds since midnight of January 1, 1970 (UTC).

4 Performance Timeline

4.1 The Performance Timeline

All interfaces that participate in the Performance Timeline, such as the PerformanceResourceTiming, PerformanceMark, and PerformanceMeasure interfaces, must adhere to the following rules:

• Must extend the PerformanceEntry interface
• Must support the getEntries, getEntriesByType, and getEntriesByName methods
• Must expose a metric name on window.performance like so:

  const unsigned short PERF_[METRIC] = [VALUE],

  where [METRIC] is the metric name and [VALUE] is a unique unsigned short that has not been already taken by another metric name.

4.2 The PerformanceEntry interface

interface PerformanceEntry {
  readonly attribute DOMString name;
  readonly attribute unsigned long long startTime;
  readonly attribute unsigned short entryType;
  readonly attribute unsigned long long duration;
};

name attribute

The name attribute must return the identifier for this PerformanceEntry object. This identifier does not have to be unique.

startTime attribute

The startTime attribute must return the first recorded timestamp of this performance metric.

entryType attribute

The entryType attribute must return a const unsigned short exposed on window.performance that defines the type of the interface represented by this PerformanceEntry object.

duration attribute

The duration attribute must return 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.

4.3 The PerformanceEntryList interface

interface PerformanceEntryList {
  readonly attribute unsigned long length;
  PerformanceEntry item(in unsigned long index);
};

The PerformanceEntryList interface defines an array of PerformanceEntry objects.

length attribute

The length attribute must return the number of PerformanceEntry objects in the PerformanceEntryList.

4.4 The window.performance attribute

interface Performance {
  PerformanceEntryList getEntries();
  PerformanceEntryList getEntriesByType(in unsigned short entryType);
  PerformanceEntryList getEntriesByName(in DOMString name, in optional unsigned short entryType);
};

The window.performance attribute provides a hosting area for performance measurement related attributes and methods.

4.5 The PerformanceTiming interface

The PerformanceTiming interface does not extend the PerformanceEntry interface. However, when the getEntriesByType and getEntriesByName methods are called with the entryType argument of PERF_NAVIGATION, a PerformanceEntryList with a PerformanceEntry object with the following values must be returned:

5 References

[IETF RFC 2119]

Key words for use in RFCs to Indicate Requirement Levels, Scott Bradner, Author. Internet Engineering Task Force, March 1997. Available at http://www.ietf.org/rfc/rfc2119.txt.

[IETF RFC 2616]

Hypertext Transfer Protocol -- HTTP/1.1, R. Fielding et al., Authors. Internet Engineering Task Force, June 1999. Available at http://www.ietf.org/rfc/rfc2616.txt.

[DOM Level 3 Core]

Document Object Model Level 3 Core Specification, A. Le Hors, et al., Editors. World Wide Web Consortium, 7 April 2004. This version of the Document Object Model Level 3 Core Recommendation is http://www.w3.org/TR/2004/REC-DOM-Level-3-Core-20040407. The latest version of DOM Core is available at http://www.w3.org/TR/domcore/.

[ECMA-262]

ECMAScript Language Specification, 5^th Edition. ECMA International, Standard ECMA-262, December 2009. This version of the ECMAScript Language is available from http://www.ecma-international.org/publications/standards/Ecma-262.htm.

[HTML5]

HTML5, Ian Hickson, Editor. World Wide Web Consortium, January 2011. This version of the HTML5 is available from http://www.w3.org/TR/html5/. The latest editor's draft is available at http://dev.w3.org/html5/spec/.

[JSMEASURE]

Measuring Client-Perceived Response Times on the WWW, R. Rajamony and M. Elnozahy, The Proceedings of the 3rd USENIX Symposium on Internet Technologies and Systems (USITS), March 2001.

[Navigation Timing]

Navigation Timing, Zhiheng Wang, Editor. World Wide Web Consortium, June 2011. This version of the Navigation Timing specification is available from http://www.w3.org/TR/2011/CR-navigation-timing-20110602/. The latest version of Navigation Timing is available at http://www.w3.org/TR/navigation-timing/.

[Web IDL]

Web IDL, Cameron McCormack, Editor. World Wide Web Consortium, July 2011. This version of the Web IDL specification is available from http://www.w3.org/TR/2011/WD-WebIDL-20110712/. The latest version of Web IDL is available at http://www.w3.org/TR/WebIDL/.

Acknowledgements

I would like to offer my sincere thanks to all the people that I have been in touch with regarding this draft for their reviews and feedback.