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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 contexts such as data transfer operations specified by XMLHTTPRequest [XHR], or Media Access Events [MAE].
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 a W3C Working Draft specification of the ProgressEvent 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 draft does not imply consensus of or endorsement by the working group, and may contain minor or major errors.
This version is published as a replacement for the second W3C Working Draft and resolves all known technical issues from that draft. 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. Unless any issues are raised by review of this draft this specification will hopefully be published as a Last Call Working draft in the second quarter of 2008. Currently there are no known technical issues which are unresolved by this specification.
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 |
User agents must implement these events such that by default they events do not bubble, and are not be cancelable.
User agents must ensure that these events trigger event listeners attached
on Element nodes for that event and on the capture and target
phases.
No default action is defined for these events.
These events are in the null namespace. Two kinds of initialisation methods are provided: one in which the namespace is required (and must be null) and one which assigns the null namespace automatically, This specification does not recommend use of one method over the other, and authors may choose whichever method suits them better for any given usage.
loadstart event when a
relevant operation has begun. progress events while a network operation is taking
place.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 loadstart 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.
Where this specification repeats information from the DOM Level 3 Events specification [D3E], the repeated information in this section is informative. In the case of any conflict between the specifications the DOM Level 3 Events specification is normative.
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,
};
lengthComputableloadedtotalEvent.initEventNS(), where the value of the
namespace parameter is specified as null [D3E].
Event.initEvent()
method [D3E] for further
description of this parameter.Event.bubbles. This
parameter overrides the intrinsic bubbling behavior
of the event and determines whether the event created
will bubbleEvent.cancelable. This
parameter overrides the intrinsic cancel behavior of
the event and determines whether the event created is
cancelableEvent.initEventNS() [D3E]. Except
as described below, parameters are the same as for initProgressEvent.
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]. Specifications which have a use case for these events should define when Progress events are dispatched.
Either by reference or by direct inclusion, specifications must maintain
the requirements for and definition of the events as described in the section
The ProgressEvent events
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 loadstart 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.
Scripts may use progress events in order to provide feedback on operations performed by an application.
progress event an SVG
document. In this example, the application uses the information in progress events emitted as an image loads in order to fill a progress bar as it receives progress events. Where the size of a download is unknown or there has been no progress yet there is simply a block moving back and forth within the progress bar to indicate that there is still some kind of activity.
<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);
image.addEventListener("error",imageLoadComplete,false);
image.addEventListener("abort",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>lengthArg and
totalArg unsigned long to match everything else.stalled event?)progress events.Various editorial changes and corrections and modifications to the examples are made from draft to draft. These are not noted in the change history.
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 initial
reference material 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, Björn Hoehrmann, David Håsäther, Bj�rn Höhrmann, Bjoern H�hrmann, Anne van Kesteren, Travis Leithead, Aaron Leventhal, Jim Ley, Chrus Lilley, Cameron McCormack, 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, Gottfried Zimmermann
The editor apologises to anyone who has inadvertently been left off this list, and welcomes corrections.