Abstract
The Progress Events specification defines an abstract event interface
that can be used for measuring progress; e.g. HTTP entity body transfers.
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
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can be found in the W3C technical reports
index at http://www.w3.org/TR/.
This is the 19 October 2010 W3C Working
Draft of Progress Events. Please send comments to public-webapps@w3.org
(archived)
with [progress-events] at the start of the subject line.
This document is produced by the Web Applications (WebApps)
Working Group. The WebApps Working Group is part of the Rich Web Clients Activity
in the W3C Interaction
Domain.
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Table of Contents
1. Introduction
This section is non-normative.
This specification defines an abstract event interface — ProgressEvent — that can be used for measuring
progress. Other specifications use this specification for that purpose.
In this example XMLHttpRequest, combined with
concepts defined in this specification, and the HTML progress element are used together to display the process
of fetching a resource. [XHR] [HTML]
<!DOCTYPE html>
<title>Waiting for Magical Unicorns</title>
<progress id=p></progress>
<script>
var progressBar = document.getElementById("p"),
client = new XMLHttpRequest()
client.open("GET", "magical-unicorns")
client.onprogress = function(pe) {
if(pe.lengthComputable) {
progressBar.max = pe.total
progressBar.value = pe.loaded
}
}
client.onloadend = function(pe) {
progressBar.value = pe.loaded
}
client.send()
</script>
Fully working code would of course be more elaborate and deal with more
scenarios, such as network errors or the end user terminating the
request.
2. Common
Infrastructure
2.1. Terminology
Event is defined by DOM Events. [DOMEvents]
Content-Length and entity body are defined by HTTP. [HTTP]
Everything in this specification is normative except for diagrams,
examples, notes and sections marked non-normative.
The key word must in this document is to be interpreted as described in
RFC 2119. [RFC2119]
A user agent must also be a conforming implementation of the IDL
fragments in this specification, as described in the Web IDL
specification. [WebIDL]
2.3. Extensibility
User agents, Working Groups, and other interested parties are
strongly encouraged to discuss extensions on a relevant public
forum, preferably public-webapps@w3.org. If this is
for some reason not possible prefix the extension in some way and start
the prefix with an uppercase letter. E.g. if company Foo wants to add a
private method bar() it could be named FooBar()
to prevent clashes with a potential future standardized
bar().
3. The ProgressEvent Interface
interface ProgressEvent : Event {
readonly attribute boolean lengthComputable;
readonly attribute unsigned long long loaded;
readonly attribute unsigned long long total;
void initProgressEvent(DOMString typeArg, boolean canBubbleArg, boolean cancelableArg, boolean lengthComputableArg, unsigned long long loadedArg, unsigned long long totalArg);
};
The lengthComputable
must return true when the length of the progress is known, or false
otherwise.
The loaded must return the
current state of progression.
The total must return the
length of the progress, or zero if that is unknown.
The initProgressEvent
method must initialize the event in a manner analogous to the
similarly-named method in the DOM Events interfaces. [DOMEvents]
3.1.
Initializing ProgressEvent for HTTP Entity
Bodies
When a specification says to dispatch an HTTP entity
body progress event named e it means that an event with
the name e, which does not bubble and is not cancelable, and
which uses the ProgressEvent
interface, is to be dispatched at the indicated object, with the remaining
members of the ProgressEvent
object set as follows, depending on the entity
body involved:
lengthComputable
-
True if the length is known, or false otherwise.
loaded
-
The number of entity body octets
transferred.
total
-
The length of the entity body as given by
the Content-Length header, or zero if
it is unknown.
3.2.
Initializing ProgressEvent for other contexts
This is left as an exercise for the editor of the specification that
introduces such a context. The editor is encouraged to define it in a way
consistent with this and other specifications using the ProgressEvent interface.
3.3.
Security Considerations for Initializing ProgressEvent
For cross-origin requests some kind of opt-in, e.g. via Cross-Origin
Resource Sharing has to happen before the events are dispatched as
information would be revealed that cannot be obtained otherwise. [CORS]
4. Suggested
ProgressEvent Types
This section is non-normative.
The suggested event types for use with the ProgressEvent interface are summarized in the table below.
Specification editors are free to tune the details to their specific
scenarios, though are strongly encouraged to discuss their usage with the
W3C WebApps Working Group on public-webapps@w3.org to ensure
input from people familiar with the subject.
| Name
| Description
| Times
| When
|
loadstart
| Progress has begun.
| Once.
| First.
|
progress
| In progress.
| Zero or more.
| After loadstart has been dispatched.
|
error
| Progression failed.
| Zero or once.
| After the last progress has been
dispatched, or after loadstart has been
dispatched if progress has not been dispatched.
|
abort
| Progression is terminated.
| Zero or once.
|
load
| Progression is successful.
| Zero or once.
|
loadend
| Progress has stopped.
| Once.
| After one of error, abort, or load has been
dispatched.
|
The error, abort, and load event types are mutually exclusive.
Throughout the web platform the error, abort, and load event types have
traditionally not had a default action and did not bubble so it is
suggested that for consistency all event types using the ProgressEvent interface do not bubble and are not
cancelable.
References
Unless marked "Non-normative" these references are normative.
- [CORS]
- (Non-normative) Cross-Origin Resource
Sharing (work in progress), A. van Kesteren. W3C.
- [DOMEvents]
- Document
Object Model (DOM) Level 2 Events Specification, T. Pixley.
W3C.
- [HTML]
- (Non-normative) HTML5 (work in
progress), I. Hickson. W3C.
- (Non-normative) HTML,
I. Hickson. WHATWG.
- [HTTP]
- Hypertext Transfer
Protocol -- HTTP/1.1, R. Fielding, J. Gettys, J. Mogul, H.
Frystyk, L. Masinter, P. Leach, T. Berners-Lee. IETF.
- [RFC2119]
- Key words for use
in RFCs to Indicate Requirement Levels, S. Bradner. IETF.
- [WebIDL]
- Web
IDL (work in progress), C. McCormack. W3C.
- [XHR]
- (Non-normative) XMLHttpRequest
(work in progress), A. van Kesteren. W3C.
Acknowledgments
The editor would like to thank Aaron Leventhal, Alan Schepers, Alex
Danilo, Andrew Emmons, Andrew Shellshear, Andy Sledd, Arthur Barstow,
Björn Höhrmann, Boris Zbarsky, Cameron McCormack, Chris Lilley,
David Håsäther, Doug Schepers, Ellen Siegel, Erik
Dahlström, Garrett Smith, Gorm Eriksen, Gottfried Zimmermann, Ian
Hickson, Jean-Claude Duford, Jean-Yves Bitterlich, Jim Ley, João
Eiras, Kartikaya Gupta, Lisa Seeman, Maciej Stachowiak, Marcos Caceres,
Michael Antony Puls, Nandini Ramani, Olli Pettay, Philip Jägenstedt,
Rich Schwerdtfeger, Robert Sayre, Robin Berjon, Simon Pieters, Suresh
Chitturi, and Travis Leithead for their contributions to this
specification.
Special thanks to the SVG WG for drafting the original ProgressEvent interface as part of the SVG
Micro DOM.
Thanks also to all those who have helped to improve this specification
by sending suggestions and corrections. (Please, keep bugging us with your
issues!)