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This document describes event types that can be used for monitoring the progress of an operation. It is primarily intended for data transfer operations such as XMLHTTPRequest [XHR], but should be usable in other relevant contexts.
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 document is the First Public Working Draft specification of the Progress events from the Web API group, part of the Rich Web Client Activity. It defines events which can be used to monitor a process and provide feedback to a user, particularly for network-based events. This editor's draft does not imply any consensus of or endorsement by any member of the working group, and may contain minor or major errors.
This document is published to solicit comments from interested parties. All comments are welcome and may be sent to public-webapi@w3.org. All messages received at this address are viewable in a public archive. The group hopes to resolve all outstanding issues and publish a Last Call draft by June 2007. Currently there are several known issues which are unresolved by this specification. These may be identified in the draft thus: @@issue: Something that needs to be settled before the draft is ready for Last Call, and may be logged in the WebAPI group's issue tracker for the ProgressEvents. The current Editor's draft (the most current version, but most prone to contain errors or be changed) is also available, with the latest version at http://dev.w3.org/cvsweb/~checkout~/2006/webapi/progress/Progress.html.
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.
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.
The terms must, should, may, must not, should not, are used in this document in accordance with [RFC2119]. A conformant implementation of this specification meets all relevant requirements identified by the use of these terms.
There are three classes of conformance to this specification:
ProgressEvent eventsThe following events are defined in this specification
| Name | Description | How often? | When? |
|---|---|---|---|
loadstart |
The operation has begun | once | Must be dispatched first |
progress |
The operation is in progress | zero or more | May be dispatched zero or more times after a loadstart
event, before any of error, abort or load events are dispatched |
error |
The operation failed to complete, e.g. as a result of a network error | never or once | Exactly one of these must be dispatched |
abort |
The operation was cancelled, e.g. as a result of user interaction | never or once | |
load |
The operation successfuly completed | never or once |
These events must not bubble, and must be cancelable.
These events trigger event listeners attached on Element
nodes for that event and on the capture and target phases. @@issue: on anything else?
No default action is defined for these events.
These events are in the null namespace. Initialisation methods are provided in both namespaced and un-namespaced versions, but this specification does not recommend use of one over the other.
@@issue: clarify that this section inherits from event.initEvent [@@]. Where there is any conflict, that should be the normative version.
interface ProgressEvent : events::Event {
readonly attribute boolean lengthComputable;
readonly attribute unsigned long loaded;
readonly attribute unsigned long total;
void initProgressEvent(in DOMString typeArg,
in boolean canBubbleArg,
in boolean cancelableArg,
in boolean lengthComputableArg,
in unsigned long loadedArg,
in unsigned long totalArg,
void initProgressEventNS(in DOMString namespaceURI,
in DOMString typeArg,
in boolean canBubbleArg,
in boolean cancelableArg,
in boolean lengthComputableArg,
in unsigned long loadedArg,
in unsigned long totalArg,
};
A progress event occurs when the user agent makes progress in some data transfer operation, such as loading a resource from the web via XMLHttpRequest [XHR]. Other specifications which have a use case for these events should define when ProgressEvent events are dispatched.
start event when a
relevant operation has begun. progress events while a network operation is taking
place. @@issue: should we require some firing
frequency for the progress type events?error event, if the failure to complete
was due to an error (such as a timeout, or network error), or an
abort event if the operation was deliberately cancelled
(e.g. by user interaction or through a script call).load event. In short, there must be at least one start event, followed by
zero or more progress events, followed by one event which may be
any of error, abort or load, according
to the outcome of the operation.
This example is informative and does not necessarily illustrate best practice.
FooAPI has a sendAndRetrieve() method, which sends some
content via a predefined SMTP server and retrieves some other content via
HTTP HEAD from a URI given as a parameter. It specifies two event targets
send and receive. Progress events as specified in
the ProgressEvent events specification may be dispatched on these targets for
the send and receive phases respectively. If any progress events are
dispatched, then at least one start event, and one of
error, abort, or load must be
dispatched on each target. For the send phase, the total
attribute of the progress events measures the size of the RFC822 message
body. For the receive phase, the total attribute specifies the size of the
content to be returned in the HTTP HEAD operation.
Below is an example of a progress event being used to update
a progress bar in an SVG document. Where the size of a download is unknown
there is simply an animation.
<svg xmlns="http://www.w3.org/2000/svg" version="1.1"
xmlns:xlink="http://www.w3.org/1999/xlink"
viewbox="0 0 400 400">
<script type="application/ecmascript"><![CDATA[
var xlinkNS = "http://www.w3.org/1999/xlink"
function showImage(imageHref) {
var image = document.getElementById('myImage');
image.setAttributeNS(xlinkNS, "href", imageHref);
image.addEventListener("progress",imageLoadProgress,false);
image.addEventListener("load",imageLoadComplete,false);
}
function imageLoadProgress(evt) {
if (evt.lengthComputable && evt.total != 0) { // we know the size, don't divide by zero
var progressBar = document.getElementById('progressBar');
progressBar.setAttribute("width", 100*evt.loaded/evt.total);
var loadAnimation = document.getElementById('loadAnimation');
loadAnimation.endElement();
} else { // we don't know the size and we need not to divide by zero
var progressBar = document.getElementById('progressBar');
progressBar.setAttribute("width", 20);
var loadAnimation = document.getElementById('loadAnimation');
loadAnimation.beginElement();
}
}
function imageLoadComplete(evt) {
var progressBar = document.getElementById('progressBar');
progressBar.setAttribute("width", 100);
var loadAnimation = document.getElementById('loadAnimation');
loadAnimation.endElement();
}
]]></script>
<image id="myImage" xlink:href="imageA.png" width="300" height="400"/>
<rect onclick="showImage('imageB.png')" width="120"
height="30" y="400" id="button" />
<animate id="loadAnimation" xlink:href="#progressBar" attributeName="x"
by="80" dur="1s" begin="button.click" repeatCount="indefinite"/>
<g id="meter" opacity="0">
<set attributeName="opacity" to=".7" begin="button.click" end="myImage.load"/>
<rect width="101" fill="none" height="5" x="5" y="5" stroke-width="1"/>
<rect id="progressBar" fill="#444" height="4" x="5.5" y="5.5"/>
</g>
</svg>Element nodeslengthComputable back to IDL definitions
toolengthComputable backtotal and
loadedpreload and postload event
types, added uploadprogresslengthComputable attributetotal as zero if it is
unknownVarious editorial changes and corrections and modifications to the examples are made from draft to draft. These are not noted in the change history.
progress
event in SVG 1.2 Drafts.progress element
proposed by WHAT-WGThe editor would like to thank the SVG working group for producing the
draft [SVGD] that this was initially based on. The
WHATWG's proposed progress element [WPE] and
the documentation for Internet Explorer's onProgress
implementation [IEoP] were also useful as an initial
reference for this specification. In addition, the following individuals'
comments have been invaluable in preparing this draft:
Robin Berjon, Jean-Yves Bitterlich, Marcos Caceres, Suresh Chitturi, Alex Danilo, Erik Dahlström, Jean-Claude Duford, Andrew Emmons, João Eiras, Gorm Eriksen, Ian Hickson, Bjoern Hoehrmann, David Håsäther, Bjoern Höhrmann, Anne van Kesteren, Travis Leithead, Aaron Leventhal, Jim Ley, Chris Lilley, Michael Antony Puls, Nandini Ramani, Robert Sayre, Alan Schepers, Doug Schepers, Rich Schwerdtfeger, Lisa Seeman, Andrew Shellshear, Ellen Siegel, Andy Sledd, Maciej Stachowiak, Boris Zbarsky
The editor apologises if anyone has been inadvefrtently left off this list, and welcomes corrections.