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This specification defines an interface for web applications to access timing information related to navigation and elements.
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 "Navigation Timing".
This is a work in progress!
If you're looking for the latest thoughts of the Web Performance Working Group participants, please look at the editor's draft instead.
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. The Working Group expects to advance this Working Draft to Recommendation Status.
Please send comments to public-web-perf@w3.org (archived) with [NavigationTiming] at the start of the subject line.
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.
This section is non-normative.
User latency is an important quality benchmark for Web Applications. While JavaScript-based mechanisms can provide comprehensive instrumentation for user latency measurements within an application, in many cases, they are unable to provide a complete end-to-end latency picture.
For example, the following Javascript shows the time it take to fully load a page:
<html>
<head>
<script type="text/javascript">
var start = new Date().getTime();
function onLoad() {
var now = new Date().getTime();
var latency = now - start;
alert("page loading time: " + latency);
}
</script>
</head>
<body onload="onLoad()">
<!- Main page body goes from here. -->
</body>
</html>
The script calculates the time it takes to load the page after the first bit of JavaScript in the head is executed, but it does not give any information about the time it takes to get the page from the server.
To address the need for complete information on user experience, this document introduces the NavigationTiming interfaces. This interface allows JavaScript mechanisms to provide complete client-side latency measurements within applications. With the proposed interface, the previous example can be modified to measure a user's perceived page load time.
The following script calculates how much time to load a page since the most recent navigation.
<html>
<head>
<script type="text/javascript">
function onLoad() {
var now = new Date().getTime();
var page_load_time = now - performance.timing.navigationStart;
alert("User-perceived page loading time: " + page_load_time);
}
<script>
</head>
<body onload="onLoad()">
<!- Main page body goes from here. -->
</body>
</html>
The interface provided by this work does not intend to be used as any sort of performance benchmark for user agents.
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 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.
Unless otherwise specified, in rest of this work, time is measured in milliseconds since midnight of January 1, 1970 (UTC).
This section is non-normative
This specification introduces an interface that provides Web applications with timing-related information. This specification does not cover how Web applications leverage these interfaces to collect, store and report the provided information.
NavigationTiming interfaceinterface NavigationTiming {
readonly attribute unsigned long long navigationStart;
readonly attribute unsigned long long unloadEventStart;
readonly attribute unsigned long long unloadEventEnd;
readonly attribute unsigned long long redirectStart;
readonly attribute unsigned long long redirectEnd;
readonly attribute unsigned long long fetchStart;
readonly attribute unsigned long long domainLookupStart;
readonly attribute unsigned long long domainLookupEnd;
readonly attribute unsigned long long connectStart;
readonly attribute unsigned long long connectEnd;
readonly attribute unsigned long long requestStart;
readonly attribute unsigned long long responseStart;
readonly attribute unsigned long long responseEnd;
readonly attribute unsigned long long domLoading;
readonly attribute unsigned long long domInteractive;
readonly attribute unsigned long long domContentLoadedEventStart;
readonly attribute unsigned long long domContentLoadedEventEnd;
readonly attribute unsigned long long domComplete;
readonly attribute unsigned long long loadEventStart;
readonly attribute unsigned long long loadEventEnd;
};
navigationStart attributeThis attribute must return the time immediately after the user agent finishes prompting to unload the previous document. If there is no previous document, this attribute must return the same value as fetchStart.
unloadEventStart attributeIf the previous document and the current document have the same origin, this attribute must return the time immediately before the user agent starts unloading the previous document. If there is no previous document or the previous document has a different origin than the current document, this attribute must return zero.
unloadEventEnd attributeIf the previous document and the current document have the same origin, this attribute must return the time immediately after the user agent finishes unloading the previous document. If there is no previous document or the previous document has a different origin than the current document or the unload is not yet completed, this attribute must return zero.
redirectStart attribute If there are HTTP redirects or equivalent when navigating and if the document before the redirect and the document at the end of the redirect are from the same origin, this attribute must return the starting time of the navigation that intiates the redirect. Otherwise, this attribute must return zero.
redirectStart is the equivalent of the navigationStart attribute of the navigation that initiates the redirect.
redirectEnd attribute If there are HTTP redirects or equivalent when navigating and if the document before the redirect and the document at the end of the redirect are from the same origin, this attribute must return the time immediately after receiving the last byte of the response of the last redirect. Otherwise, this attribute must return zero.
redirectEnd is the equivalent of the responseEnd attribute of the last redirect.
The relaxed same orgin policy doesn't provide sufficient protection against unauthorized visits accross documents. In shared hosting, an untrusted third party is able to host an HTTP server at the same IP address but on a different port.
fetchStart attributeIf the new resource is to be fetched using HTTP GET or equivalent, fetchStart must return the time immediately before the user agent starts checking any relevant application caches. Otherwise, it must return the time when the user agent starts fetching the resource.
domainLookupStart attributeThis attribute must return the time immediately before the user agent starts the domain name lookup for the current document. If the current document is retrieved from relevant application caches or local resources, this attribute must return the same value as fetchStart.
domainLookupEnd attributeThis attribute must return the time immmediately after the user agent finishes the domain name lookup for the current document. If the current document is retrieved from relevant application caches or local resources, this attribute must return the same value as fetchStart.
This section is non-normative.
Checking and retrieving contents from the HTTP cache [RFC 2616] is part of the fetching process. It's covered by the requestStart, responseStart and responseEnd attributes.
In case where the user agent already has the domain information in cache, domainLookupStart and domainLookupEnd represent the times when the user agent starts and ends the domain data retrieval from the cache.
connectStart attributeThis attribute must return the time immediate before the user agent start establishing the connection to the server to retrieve the document. If a persistent connection [RFC 2616] is used or the current document is retrieved from relevant application caches or local resources, this attribute must return value of domainLookupEnd.
connectEnd attribute This attribute must return the time immediately after the user agent finishes establishing the connection to the server to retrieve the current document. If a persistent connection [RFC 2616] is used or the current document is retrieved from relevant application caches or local resources, this attribute must return the value of domainLookupEnd
If the transport connection fails and the user agent reopens a connection, connectStart and connectEnd should return the corresponding values of the new connection.
connectEnd must include the time interval to establish the transport connection. It must not include other time interval such as SSL handshake and SOCKS authentication.
requestStart attributeThis attribute must return the time immediate before the user agent starts requesting the current document.
If the transport connection fails after a request is sent and the user agent reopens a connection and resend the request, requestStart should return the corresponding values of the new request.
requestStart is prior to checking HTTP cache.
responseStart attribute This attribute must return the time immediate after the user agent receives the first byte of the response from the server, or from relevant application caches or from local resources.
responseEnd attributeThis attribute must return the time immediately after the user agent receives the last byte of the current document or immediately before the transport connection is closed, whichever comes first. The document here can be received either from the server, relevant application caches or from local resources.
domLoading attributeThis attribute must return the time immediately before the user agent sets the current document readiness to "loading".
domInteractive attributeThis attribute must return the time immediately before the user agent sets the current document readiness to "interactive".
domContentLoadedEventStart attributeThis attribute must return the time immediately before the user agent fires the DOMContentLoaded event at the Document.
domContentLoadedEventEnd attributeThis attribute must return the time immediately after the document's DOMContentLoaded event completes.
domComplete attributeThis attribute must return the time immediately before the user agent sets the current document readiness to "complete".
If the current document readiness changes to the same state multiple times, domLoading, domInteractive, domContentLoadedEventStart, domContentLoadedEventEnd and domComplete must return the time of the first occurrence of the corresponding document readiness change.
loadEventStart attribute This attribute must return the time immediately before the load event of the the current document is fired. It must return zero when the load event is not fired yet.
loadEventEnd attributeThis attribute must return the time when the load event of the current document is completed. It must return zero when the load event is not fired or is not completed.
NavigationInfo interfaceinterface NavigationInfo {
const unsigned short TYPE_NAVIGATE = 0;
const unsigned short TYPE_RELOAD = 1;
const unsigned short TYPE_BACK_FORWARD = 2;
const unsigned short TYPE_RESERVED = 255;
readonly attribute unsigned short type;
readonly attribute unsigned short redirectCount;
};
type attributeThis attribute must return the type of the last non-redirect navigation in the current browsing context. It must have one of the following navigation type values.
redirectCount attribute This attribute must return the number of redirects since the last non-redirect navigation under the current browsing context. If there is no redirect, this attribute must return zero.
window.performance
attributeinterface Performance {
readonly attribute NavigationTiming timing;
readonly attribute NavigationInfo navigation;
};
[Supplemental]
interface Window {
readonly attribute Performance performance;
};
The window.performance attribute provides a hosting area for performance related attributes. Specifically, the window.performance.timing attribute represents the timing information related to the browsing contexts since the last non-redirect navigation. Each browsing context must have a unique window.performance.timing attribute. NavigationTiming objects in the timing attribute must be sorted by the chronological order of the corresponding browsing context.
Following is an example of how to use the interface in an HTML page:
var t = performance.timing;
var n = performance.navigation;
if (t.loadEventEnd > 0) {
var page_load_time = t.loadEventEnd - t.navigationStart;
if (n.type == n.TYPE_NAVIGATE) {
alert (page_load_time);
}
}
All the attributes in window.performance.timing and window.performance.navigation should not be written to until the Window object of the current document is created, even though their attributes are referred to in the following steps to facilitate description.
A user agent may maintain instances of the NavigationTiming and NavigationInfo interfaces until the Window object associated with the current document is created, when window.performance.timing and window.performance.navigation are replaced with these instances.
This secion is non-normative.
The following graph illustrates the timing attributes defined by the NavigationTiming interface and the NavigationInfo interface. Attributed underlined are only available when the previous document and the current document are from the same origin. User agents may perform internal processing in between timings, which allow for non-normative intervals between timings.
Return to step 11 if the user agent fails to send the request or receive the entire response, and needs to reopen the connection.
When persistent connection [RFC 2616] is enabled, a user agent may first try to re-use an open connect to send the request while the connection can be asynchronously closed. In such case, connectStart, connectEnd, requestStart and requestEnd should represent timing information collected over the re-open connection.
The accuracy of the timing-related attributes in the NavigationTiming interfaces is recommended to be one millisecond or finer.
Some user agents maintain the DOM structure of the document in memory during navigation operations such as forward and backward. In those cases, the window.performance.timing and window.performance.navigation objects much not be altered during the navigation.
There are implied strong references from the window object to its window.performance.timing and window.performance.navigation objects.
This section is non-normative.
This section is non-normative.
I would like to offer my sincere thanks to all the people that I have been in touch with regarding this draft, including Anderson Quach, Alex Russell, Alois Reitbauer, Annie Sullivan, Christian Biesinger, Darin Fisher, Eric Lawrence, Jason Weber, Jonas Sicking, Kyle Scholz, Lenny Rachitsky, Nic Jansma, Richard Rabbat, Sergey Novikov, Steve Souders, Tony Gentilcore for their reviews and feedbacks.