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<pre class="metadata">
Indent: 2
Title: File API
Shortname: fileapi
Level: 1
Group: webplatform
Editor: Arun Ranganathan, Mozilla Corporation, http://arunranga.com/, arun@mozilla.com
Editor: Marijn Kruisselbrink, Google, mek@chromium.org
Status: ED
ED: https://w3c.github.io/FileAPI/
TR: http://www.w3.org/TR/FileAPI/
Repository: w3c/FileAPI
Previous Version: http://www.w3.org/TR/2012/WD-FileAPI-20121025/
Abstract: This specification provides an API for representing file objects in web applications,
as well as programmatically selecting them and accessing their data. This includes:
* A {{FileList}} interface, which represents an array of individually selected files from the underlying system. The user interface for selection can be invoked via <code><input type="file"></code>, i.e. when the input element is in the <code>File Upload</code> state [[HTML]].
* A {{Blob}} interface, which represents immutable raw binary data, and allows access to ranges of bytes within the {{Blob}} object as a separate {{Blob}}.
* A {{File}} interface, which includes readonly informational attributes about a file such as its name and the date of the last modification (on disk) of the file.
* A {{FileReader}} interface, which provides methods to read a {{File}} or a {{Blob}}, and an event model to obtain the results of these reads.
* A <a section href="#url">URL scheme</a> for use with binary data such as files, so that they can be referenced within web applications.
Additionally, this specification defines objects to be used within threaded web applications for the synchronous reading of files.
[[#requirements]] covers the motivation behind this specification.
This API is designed to be used in conjunction with other APIs and elements on the web platform, notably:
{{XMLHttpRequest}} (e.g. with an overloaded {{XMLHttpRequest/send()}} method for {{File}} or {{Blob}} arguments),
{{Worker/postMessage()}},
{{DataTransfer}} (part of the drag and drop API defined in [[HTML]])
and Web Workers.
Additionally, it should be possible to programmatically obtain a list of files from the <{input}> element
when it is in the <code>File Upload</code> state [[HTML]].
These kinds of behaviors are defined in the appropriate affiliated specifications.
Status Text: Previous discussion of this specification has taken place on two other mailing lists: <a href="mailto:public-webapps@w3.org">public-webapps@w3.org</a> (<a href="http://lists.w3.org/Archives/Public/public-webapps/">archive</a>) and <a href="mailto:public-webapi@w3.org">public-webapi@w3.org</a> (<a href="http://lists.w3.org/Archives/Public/public-webapi/">archive</a>). Ongoing discussion will be on the <a href="mailto:public-webapps@w3.org">public-webapps@w3.org</a> mailing list.
This draft consists of changes made to the previous Last Call Working Draft. Please send comments to the <a href="mailto:public-webapi@w3.org">public-webapi@w3.org</a> as described above. You can see Last Call Feedback on the W3C Wiki: <a href="http://www.w3.org/wiki/Webapps/LCWD-FileAPI-20130912">http://www.w3.org/wiki/Webapps/LCWD-FileAPI-20130912</a>
Translate Ids: dictdef-blobpropertybag dfn-BlobPropertyBag, dictdef-filepropertybag dfn-FilePropertyBag, filereadersync dfn-FileReaderSync, filelist dfn-filelist, filereader dfn-filereader, file dfn-file, blob dfn-Blob, blob-section blob, file-section file
Markup Shorthands: css no, markdown yes
</pre>
<pre class="link-defaults">
spec: html
type: element
text: a
text: iframe
spec: streams
type: dfn
text: chunk
spec: url
type: dfn
text: url; for:/
type: interface
text: URL
</pre>
<pre class="anchors">
spec: xhr; urlPrefix: https://xhr.spec.whatwg.org/
type: method
for: XMLHttpRequest
text: getAllResponseHeaders(); url: #dom-xmlhttprequest-getallresponseheaders
spec: html; urlPrefix: https://html.spec.whatwg.org/multipage/
urlPrefix: semantics.html
type: element-attr; for: a; text: download; url: #attr-hyperlink-download
spec: mimesniff; urlPrefix: https://mimesniff.spec.whatwg.org/
type: dfn
text: parsable mime type
text: parse a MIME type
spec: ecma-262; urlPrefix: http://tc39.github.io/ecma262/
type: interface
text: Array; url: sec-array-constructor
text: Date; url: sec-date-constructor
</pre>
<h2 id="intro">
Introduction</h2>
*This section is informative.*
Web applications should have the ability to manipulate as wide as possible a range of user input,
including files that a user may wish to upload to a remote server or manipulate inside a rich web application.
This specification defines the basic representations for files,
lists of files,
errors raised by access to files,
and programmatic ways to read files.
Additionally, this specification also defines an interface that represents "raw data"
which can be asynchronously processed on the main thread of conforming user agents.
The interfaces and API defined in this specification can be used with other interfaces and APIs exposed to the web platform.
The {{File}} interface represents file data typically obtained from the underlying file system,
and the {{Blob}} interface
("Binary Large Object" - a name originally introduced to web APIs in <a href="https://developers.google.com/gears/?csw=1">Google Gears</a>)
represents immutable raw data.
{{File}} or {{Blob}} reads should happen asynchronously on the main thread,
with an optional synchronous API used within threaded web applications.
An asynchronous API for reading files prevents blocking and UI "freezing" on a user agent's main thread.
This specification defines an asynchronous API based on an *event model*
to read and access a {{File}} or {{Blob}}’s data.
A {{FileReader}} object provides asynchronous read methods to access that file's data
through event handler content attributes and the firing of events.
The use of events and event handlers allows separate code blocks the ability
to monitor the *progress of the read*
(which is particularly useful for remote drives or mounted drives,
where file access performance may vary from local drives)
and error conditions that may arise during reading of a file.
An example will be illustrative.
<div class="example">
In the example below, different code blocks handle progress, error, and success conditions.
<pre highlight="js">
function startRead() {
// obtain input element through DOM
var file = document.getElementById('file').files[0];
if(file){
getAsText(file);
}
}
function getAsText(readFile) {
var reader = new FileReader();
// Read file into memory as UTF-16
reader.readAsText(readFile, "UTF-16");
// Handle progress, success, and errors
reader.onprogress = updateProgress;
reader.onload = loaded;
reader.onerror = errorHandler;
}
function updateProgress(evt) {
if (evt.lengthComputable) {
// evt.loaded and evt.total are ProgressEvent properties
var loaded = (evt.loaded / evt.total);
if (loaded < 1) {
// Increase the prog bar length
// style.width = (loaded * 200) + "px";
}
}
}
function loaded(evt) {
// Obtain the read file data
var fileString = evt.target.result;
// Handle UTF-16 file dump
if(utils.regexp.isChinese(fileString)) {
//Chinese Characters + Name validation
}
else {
// run other charset test
}
// xhr.send(fileString)
}
function errorHandler(evt) {
if(evt.target.error.name == "NotReadableError") {
// The file could not be read
}
}
</pre>
</div>
<h2 id="terminology">
Terminology and Algorithms</h2>
When this specification says to <dfn id="terminate-an-algorithm" lt="terminate an algorithm|terminate this algorithm">terminate an algorithm</dfn>
the user agent must terminate the algorithm after finishing the step it is on.
Asynchronous <a>read methods</a> defined in this specification may return before the algorithm in question is terminated,
and can be terminated by an {{FileReader/abort()}} call.
The algorithms and steps in this specification use the following mathematical operations:
* max(a,b) returns the maximum of a and b,
and is always performed on integers as they are defined in WebIDL [[WebIDL]];
in the case of max(6,4) the result is 6.
This operation is also defined in ECMAScript [[!ECMA-262]].
* min(a,b) returns the minimum of a and b,
and is always performed on integers as they are defined in WebIDL [[WebIDL]];
in the case of min(6,4) the result is 4.
This operation is also defined in ECMAScript [[ECMA-262]].
* Mathematical comparisons such as < (less than), ≤ (less than or equal to), and > (greater than) are as in ECMAScript [[ECMA-262]].
The term <dfn id="UnixEpoch">Unix Epoch</dfn> is used in this specification to refer to the time 00:00:00 UTC on January 1 1970
(or 1970-01-01T00:00:00Z ISO 8601);
this is the same time that is conceptually "<code>0</code>" in ECMA-262 [[ECMA-262]].
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<h2 id="blob-section">
The Blob Interface and Binary Data</h2>
A {{Blob}} object refers to a <a>byte</a> sequence,
and has a {{Blob/size}} attribute which is the total number of bytes in the byte sequence,
and a {{Blob/type}} attribute,
which is an ASCII-encoded string in lower case representing the media type of the <a>byte</a> sequence.
A {{Blob}} must have a <dfn id="readabilityState" for="Blob">readability state</dfn>,
which is one of <a><code>OPENED</code></a> or <a for="Blob/readability state"><code>CLOSED</code></a>.
A {{Blob}} that refers to a <a>byte</a> sequence,
including one of 0 bytes,
is said to be in the <dfn id="dfn-openState" for="Blob/readability state"><code>OPENED</code></dfn> <a>readability state</a>.
A {{Blob}} is said to be <dfn id="closed" for=Blob>closed</dfn> if its {{Blob/close()}} method has been called.
A {{Blob}} that is <a for=Blob>closed</a> is said to be in the <dfn id="dfn-closedState" for="Blob/readability state"><code>CLOSED</code></dfn> <a>readability state</a>.
Each {{Blob}} must have an internal <dfn id="snapshot-state" for=Blob>snapshot state</dfn>,
which must be initially set to the state of the underlying storage,
if any such underlying storage exists,
and must be preserved through <a abstract-op>StructuredClone</a>.
Further normative definition of <a>snapshot state</a> can be found for {{File}}s.
<pre class="idl">
[Constructor(optional sequence<BlobPart> blobParts, optional BlobPropertyBag options),
Exposed=(Window,Worker)]
interface Blob {
readonly attribute unsigned long long size;
readonly attribute DOMString type;
readonly attribute boolean isClosed;
//slice Blob into byte-ranged chunks
Blob slice([Clamp] optional long long start,
[Clamp] optional long long end,
optional DOMString contentType);
void close();
};
dictionary BlobPropertyBag {
DOMString type = "";
};
typedef (BufferSource or Blob or USVString) BlobPart;
</pre>
<h3 id="constructorBlob">
Constructors</h3>
The {{Blob()}} constructor can be invoked with zero or more parameters.
When the {{Blob()}} constructor is invoked,
user agents must run the following steps:
1. If invoked with zero parameters,
return a new {{Blob}} object with its <a>readability state</a> set to <a><code>OPENED</code></a>,
consisting of 0 bytes,
with {{Blob/size}} set to 0,
and with {{Blob/type}} set to the empty string.
2. Otherwise, the constructor is invoked with a {{blobParts}} sequence. Let |a| be that sequence.
3. Let |bytes| be an empty sequence of bytes.
4. Let |length| be |a|'s length.
For 0 ≤ |i| < |length|, repeat the following steps:
1. Let |element| be the |i|th element of |a|.
2. If |element| is a {{USVString}}, run the following substeps:
1. Append the result of [=UTF-8 encoding=] |s| to |bytes|.
Note: The algorithm from WebIDL [[WebIDL]] replaces unmatched surrogates in an invalid utf-16 string
with U+FFFD replacement characters.
Scenarios exist when the {{Blob}} constructor may result in some data loss
due to lost or scrambled character sequences.
3. If |element| is a {{BufferSource}}, <a lt="get a copy of the buffer source">get
a copy of the bytes held by the buffer source</a>, and append those bytes to |bytes|.
4. If |element| is a {{Blob}},
append the bytes it represents to |bytes|.
The {{Blob/type}} of the {{Blob}} array element is ignored and will not affect {{Blob/type}} of returned
{{Blob}} object.
5. If the {{BlobPropertyBag/type}} member of the optional <code>options</code> argument is provided
and is not the empty string,
run the following sub-steps:
1. Let |t| be the {{BlobPropertyBag/type}} dictionary member.
If |t| contains any characters outside the range U+0020 to U+007E,
then set |t| to the empty string and return from these substeps.
2. Convert every character in |t| to [=ASCII lowercase=].
6. Return a {{Blob}} object with its <a>readability state</a> set to <a><code>OPENED</code></a>,
referring to |bytes| as its associated <a>byte</a> sequence,
with its {{Blob/size}} set to the length of |bytes|,
and its {{Blob/type}} set to the value of |t| from the substeps above.
<h4 id="constructorParams">
Constructor Parameters</h4>
The {{Blob()}} constructor can be invoked with the parameters below:
<dl>
<dt>A <dfn id="dfn-blobParts" argument for="Blob/Blob(blobParts, options)"><code>blobParts</code></dfn> <code>sequence</code>
<dd>which takes any number of the following types of elements, and in any order:
* {{BufferSource}} elements.
* {{Blob}} elements.
* {{DOMString}} elements.
<dt id="dfn-BlobPropertyBagMembers">An *optional* {{BlobPropertyBag}}
<dd>which takes one member:
* <dfn id="dfn-BPtype" dict-member for="BlobPropertyBag">type</dfn>,
the ASCII-encoded string in lower case representing the media type of the {{Blob}}.
Normative conditions for this member are provided in the [[#constructorBlob]].
</dl>
<div class="example">
Examples of constructor usage follow.
<pre class="lang-javascript">
// Create a new Blob object
var a = new Blob();
// Create a 1024-byte ArrayBuffer
// buffer could also come from reading a File
var buffer = new ArrayBuffer(1024);
// Create ArrayBufferView objects based on buffer
var shorts = new Uint16Array(buffer, 512, 128);
var bytes = new Uint8Array(buffer, shorts.byteOffset + shorts.byteLength);
var b = new Blob(["foobarbazetcetc" + "birdiebirdieboo"], {type: "text/plain;charset=utf-8"});
var c = new Blob([b, shorts]);
var a = new Blob([b, c, bytes]);
var d = new Blob([buffer, b, c, bytes]);
</pre>
</div>
<h3 id="attributes-blob">
Attributes</h3>
<dl dfn-type="attribute" dfn-for="Blob">
<dt><dfn id="dfn-size">size</dfn>
<dd>Returns the size of the <a>byte</a> sequence in number of bytes.
On getting, conforming user agents must return the total number of bytes that can be read by a {{FileReader}} or {{FileReaderSync}} object,
or 0 if the {{Blob}} has no bytes to be read.
If the {{Blob}} has a readability state of <a for="Blob/readability state"><code>CLOSED</code></a>
then {{Blob/size}} must return 0.
<dt><dfn id="dfn-type">type</dfn>
<dd>The ASCII-encoded string in lower case representing the media type of the {{Blob}}.
On getting, user agents must return the type of a {{Blob}}
as an ASCII-encoded string in lower case,
such that when it is converted to a <a>byte</a> sequence,
it is a <a>parsable MIME type</a>,
or the empty string – 0 bytes – if the type cannot be determined.
The {{Blob/type}} attribute can be set by the web application itself through constructor invocation
and through the {{Blob/slice()}} call;
in these cases, further normative conditions for this attribute are in [[#constructorBlob]],
[[#file-constructor]],
and [[#slice-method-algo]] respectively.
User agents can also determine the {{Blob/type}} of a {{Blob}},
especially if the <a>byte</a> sequence is from an on-disk file;
in this case, further normative conditions are in the <a>file type guidelines</a>.
Note: The type |t| of a {{Blob}} is considered a <a>parsable MIME type</a>,
if performing the <a>parse a MIME type</a> algorithm to a byte sequence converted from
the ASCII-encoded string representing the Blob object's type does not return undefined.
Note: Use of the {{Blob/type}} attribute informs the <a>encoding determination</a>
and <a href="#processing-media-types">parsing the Content-Type header</a>
when <a>dereferencing</a> <a>Blob URLs</a>.
<dt><dfn id="dfn-isClosed">isClosed</dfn>
<dd>The boolean value that indicates whether the {{Blob}} is in the <a for="Blob/readability state"><code>CLOSED</code></a> <a>readability state</a>.
On getting, user agents must return <code>false</code>
if the {{Blob}} is in the <a><code>OPENED</code></a> <a>readability state</a>,
and <code>true</code> if the {{Blob}} is in the <a for="Blob/readability state"><code>CLOSED</code></a> <a>readability state</a>
as a result of the {{Blob/close()}} method being called.
</dl>
<h3 id="methodsandparams-blob">
Methods and Parameters</h3>
<h4 id="slice-method-algo">
The slice method</h4>
The <dfn id="dfn-slice" method for=Blob lt="slice(start, end, contentType), slice(start, end), slice(start), slice()">slice()</dfn> method
returns a new {{Blob}} object with bytes ranging from
the optional {{start}} parameter
up to but not including the optional {{end}} parameter,
and with a {{Blob/type}} attribute that is the value of the optional {{contentType!!argument}} parameter.
It must act as follows:
1. Let |O| be the {{Blob}} <a>context object</a> on which the {{slice()}} method is being called.
2. The optional <dfn argument for="Blob/slice(start, end, contentType)" id="dfn-start">start</dfn> parameter
is a value for the start point of a {{slice()}} call,
and must be treated as a byte-order position,
with the zeroth position representing the first byte.
User agents must process {{Blob/slice()}} with {{start}} normalized according to the following:
<ol type="a">
<li>If the optional {{start}} parameter is not used as a parameter when making this call, let |relativeStart| be 0.
<li>If {{start}} is negative, let |relativeStart| be <code>max(({{Blob/size}} + {{start}}), 0)</code>.
<li>Else, let |relativeStart| be <code>min(start, size)</code>.
</ol>
3. The optional <dfn argument for="Blob/slice(start, end, contentType)" id="dfn-end">end</dfn> parameter
is a value for the end point of a {{slice()}} call.
User agents must process {{Blob/slice()}} with {{end}} normalized according to the following:
<ol type="a">
<li>If the optional {{end}} parameter is not used as a parameter when making this call, let |relativeEnd| be {{Blob/size}}.
<li>If {{end}} is negative, let |relativeEnd| be <code>max((size + end), 0)</code>.
<li>Else, let |relativeEnd| be <code>min(end, size)</code>.
</ol>
4. The optional <dfn argument for="Blob/slice(start, end, contentType)" id="dfn-contentTypeBlob">contentType</dfn> parameter
is used to set the ASCII-encoded string in lower case representing the media type of the Blob.
User agents must process the {{Blob/slice()}} with {{contentType}} normalized according to the following:
<ol type="a">
<li>If the {{contentType}} parameter is not provided, let |relativeContentType| be set to the empty string.
<li>Else let |relativeContentType| be set to {{contentType}} and run the substeps below:
1. If |relativeContentType| contains any characters outside the range of U+0020 to U+007E,
then set |relativeContentType| to the empty string and return from these substeps.
2. Convert every character in |relativeContentType| to [=ASCII lowercase=].
</ol>
5. Let |span| be <code>max((relativeEnd - relativeStart), 0)</code>.
6. Return a new {{Blob}} object |S| with the following characteristics:
<ol type="a">
<li>|S| has a <a>readability state</a> equal to that of |O|'s <a>readability state</a>.
Note: The <a>readability state</a> of the <a>context object</a> is retained
by the {{Blob}} object returned by the {{Blob/slice()}} call;
this has implications on whether the returned {{Blob}} is actually usable
for <a>read operation</a>s or as a <a>Blob URL</a>.
<li>|S| refers to |span| consecutive <a>byte</a>s from |O|,
beginning with the <a>byte</a> at byte-order position |relativeStart|.
<li>|S|.{{Blob/size}} = |span|.
<li>|S|.{{Blob/type}} = |relativeContentType|.
</ol>
<div class="example">
The examples below illustrate the different types of {{slice()}} calls possible. Since the
{{File}} interface inherits from the {{Blob}} interface, examples are based on the use of the {{File}} interface.
<pre class="lang-javascript">
// obtain input element through DOM
var file = document.getElementById('file').files[0];
if(file)
{
// create an identical copy of file
// the two calls below are equivalent
var fileClone = file.slice();
var fileClone2 = file.slice(0, file.size);
// slice file into 1/2 chunk starting at middle of file
// Note the use of negative number
var fileChunkFromEnd = file.slice(-(Math.round(file.size/2)));
// slice file into 1/2 chunk starting at beginning of file
var fileChunkFromStart = file.slice(0, Math.round(file.size/2));
// slice file from beginning till 150 bytes before end
var fileNoMetadata = file.slice(0, -150, "application/experimental");
}
</pre>
</div>
<h4 id="close-method">
The close method</h4>
The <dfn id="dfn-close" method for=Blob>close()</dfn> method is said to <a lt="closed" for=Blob>close</a> a {{Blob}},
and must act as follows:
1. If the <a>readability state</a> of the <a>context object</a> is <a for="Blob/readability state"><code>CLOSED</code></a>,
<a>terminate this algorithm</a>.
2. Otherwise, set the <a>readability state</a> of the <a>context object</a> to <a for="Blob/readability state"><code>CLOSED</code></a>.
3. If the <a>context object</a> has an entry in the <a>Blob URL Store</a>,
<a>remove the entry</a> that corresponds to the <a>context object</a>.
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<h2 id="file-section">
The File Interface</h2>
A {{File}} object is a {{Blob}} object with a {{File/name}} attribute, which is a string;
it can be created within the web application via a constructor,
or is a reference to a <a>byte</a> sequence from a file from the underlying (OS) file system.
If a {{File}} object is a reference to a <a>byte</a> sequence originating from a file on disk,
then its <a>snapshot state</a> should be set to the state of the file on disk at the time the {{File}} object is created.
Note: This is a non-trivial requirement to implement for user agents,
and is thus not a *must* but a *should* [[RFC2119]].
User agents should endeavor to have a {{File}} object's <a>snapshot state</a>
set to the state of the underlying storage on disk at the time the reference is taken.
If the file is modified on disk following the time a reference has been taken,
the {{File}}'s <a>snapshot state</a> will differ from the state of the underlying storage.
User agents may use modification time stamps and other mechanisms to maintain <a>snapshot state</a>,
but this is left as an implementation detail.
When a {{File}} object refers to a file on disk,
user agents must return the {{Blob/type}} of that file,
and must follow the <dfn export>file type guidelines</dfn> below:
* User agents must return the {{Blob/type}} as an ASCII-encoded string in lower case,
such that when it is converted to a corresponding byte sequence,
it is a <a>parsable MIME type</a>,
or the empty string – 0 bytes – if the type cannot be determined.
* When the file is of type <code>text/plain</code>
user agents must NOT append a charset parameter to the <i>dictionary of parameters</i> portion of the media type [[!MIMESNIFF]].
* User agents must not attempt heuristic determination of encoding,
including statistical methods.
<pre class="idl">
[Constructor(sequence<BlobPart> fileBits,
USVString fileName,
optional FilePropertyBag options),
Exposed=(Window,Worker)]
interface File : Blob {
readonly attribute DOMString name;
readonly attribute long long lastModified;
};
dictionary FilePropertyBag : BlobPropertyBag {
long long lastModified;
};
</pre>
<h3 id="file-constructor">
Constructor</h3>
The {{File}} constructor is invoked with two or three parameters,
depending on whether the optional dictionary parameter is used.
When the {{File()}} constructor is invoked,
user agents must run the following steps:
1. Let |a| be the {{fileBits}} sequence argument.
Let |bytes| be an empty sequence of <a>byte</a>.
Let |length| be |a|'s length.
For 0 ≤ i < |length|, repeat the following steps:
1. Let |element| be the |i|'th element of |a|.
2. If |element| is a {{USVString}}, run the following substeps:
1. Append the result of [=UTF-8 encoding=] |s| to |bytes|.
Note: The algorithm from WebIDL [[WebIDL]] replaces unmatched surrogates in an invalid utf-16 string with U+FFFD replacement characters.
Scenarios exist when the {{Blob}} constructor may result in some data loss due to lost or scrambled character sequences.
3. If |element| is a {{BufferSource}}, <a lt="get a copy of the buffer source">get
a copy of the bytes held by the buffer source</a>, and append those bytes to |bytes|.
4. If |element| is a {{Blob}},
append the bytes it represents to |bytes|.
The {{Blob/type}} of the {{Blob}} argument must be ignored.
2. Let |n| be a new string of the same size as the {{fileName}} argument to the constructor.
Copy every character from {{fileName}} to |n|,
replacing any "/" character (U+002F SOLIDUS) with a ":" (U+003A COLON).
Note: Underlying OS filesystems use differing conventions for file name;
with constructed files, mandating UTF-16 lessens ambiquity when file names are converted to <a>byte</a> sequences.
3. If the optional {{FilePropertyBag}} dictionary argument is used,
then run the following substeps:
1. If the {{BlobPropertyBag/type}} member is provided and is not the empty string,
let |t| be set to the {{BlobPropertyBag/type}} dictionary member.
If |t| contains any characters outside the range U+0020 to U+007E,
then set |t| to the empty string and return from these substeps.
2. Convert every character in |t| to [=ASCII lowercase=].
3. If the {{FilePropertyBag/lastModified}} member is provided,
let |d| be set to the {{FilePropertyBag/lastModified}} dictionary member.
If it is not provided,
set |d| to the current date and time
represented as the number of milliseconds since the <a>Unix Epoch</a>
(which is the equivalent of <code>Date.now()</code> [[ECMA-262]]).
Note: Since ECMA-262 {{Date}} objects convert to <code>long long</code> values
representing the number of milliseconds since the <a>Unix Epoch</a>,
the {{FilePropertyBag/lastModified}} member could be a {{Date}} object [[ECMA-262]].
4. Return a new {{File}} object |F| such that:
1. |F| has a <a>readability state</a> of <a><code>OPENED</code></a>.
2. |F| refers to the |bytes| <a>byte</a> sequence.
3. |F|.{{Blob/size}} is set to the number of total bytes in |bytes|.
4. |F|.{{File/name}} is set to |n|.
5. |F|.{{Blob/type}} is set to |t|.
6. |F|.{{File/lastModified}} is set to |d|.
<h4 id="file-constructor-params">
Constructor Parameters</h4>
The {{File()}} constructor can be invoked with the parameters below:
<dl>
<dt>A <dfn id="dfn-fileBits" argument for="File/File(fileBits, fileName, options)"><code>fileBits</code></dfn> <code>sequence</code>
<dd>which takes any number of the following elements, and in any order:
* {{BufferSource}} elements.
* {{Blob}} elements, which includes {{File}} elements.
* {{DOMString}} elements.
<dt>A <dfn id="dfn-fileName" argument for="File/File(fileBits, fileName, options)"><code>fileName</code></dfn> parameter
<dd>A {{USVString}} parameter representing the name of the file;
normative conditions for this constructor parameter can be found in [[#file-constructor]].
<dt id="def-Properties">An optional {{FilePropertyBag}} dictionary
<dd>which in addition to the <a href="#dfn-BlobPropertyBagMembers">members</a> of
{{BlobPropertyBag}} takes one member:
* An optional <dfn dict-member for=FilePropertyBag id="dfn-FPdate">lastModified</dfn> member,
which must be a <code>long long</code>;
normative conditions for this member are provided in [[#file-constructor]].
</dl>
<h3 id="file-attrs">
Attributes</h3>
<dl dfn-type=attribute dfn-for=File>
<dt><dfn id="dfn-name">name</dfn>
<dd>The name of the file.
On getting, this must return the name of the file as a string.
There are numerous file name variations and conventions used by different underlying OS file systems;
this is merely the name of the file, without path information.
On getting, if user agents cannot make this information available,
they must return the empty string.
If a {{File}} object is created using a constructor,
further normative conditions for this attribute are found in [[#file-constructor]].
<dt><dfn id="dfn-lastModified">lastModified</dfn>
<dd>The last modified date of the file.
On getting, if user agents can make this information available,
this must return a <code>long long</code> set to the time the file was last modified
as the number of milliseconds since the <a>Unix Epoch</a>.
If the last modification date and time are not known,
the attribute must return the current date and time
as a <code>long long</code> representing the number of milliseconds since the <a>Unix Epoch</a>;
this is equivalent to <code class="lang-javascript">Date.now()</code> [[ECMA-262]].
If a {{File}} object is created using a constructor,
further normative conditions for this attribute are found in [[#file-constructor]].
</dl>
The {{File}} interface is available on objects that expose an attribute of type {{FileList}};
these objects are defined in HTML [[HTML]].
The {{File}} interface, which inherits from {{Blob}}, is immutable,
and thus represents file data that can be read into memory at the time a <a>read operation</a> is initiated.
User agents must process reads on files that no longer exist at the time of read as <a lt="file read error">errors</a>,
throwing a {{NotFoundError}} exception
if using a {{FileReaderSync}} on a Web Worker [[Workers]]
or firing an {{error!!event}} event
with the {{error!!attribute}} attribute returning a {{NotFoundError}}.
<div class="example">
In the examples below, metadata from a file object is displayed meaningfully, and a file object is created with a name and a last modified date.
<pre class="lang-javascript">
var file = document.getElementById("filePicker").files[0];
var date = new Date(file.lastModified);
println("You selected the file " + file.name + " which was modified on " + date.toDateString() + ".");
...
// Generate a file with a specific last modified date
var d = new Date(2013, 12, 5, 16, 23, 45, 600);
var generatedFile = new File(["Rough Draft ...."], "Draft1.txt", {type: "text/plain", lastModified: d})
...
</pre>
</div>
<h2 id="filelist-section">
The FileList Interface</h2>
Note: The {{FileList}} interface should be considered "at risk"
since the general trend on the Web Platform is to replace such interfaces
with the {{Array}} platform object in ECMAScript [[ECMA-262]].
In particular, this means syntax of the sort <code class="lang-javascript">filelist.item(0)</code> is at risk;
most other programmatic use of {{FileList}} is unlikely to be affected by the eventual migration to an {{Array}} type.
This interface is a list of {{File}} objects.
<pre class="idl">
[Exposed=(Window,Worker)]
interface FileList {
getter File? item(unsigned long index);
readonly attribute unsigned long length;
};
</pre>
<div class="example">
Sample usage typically involves DOM access to the <code><input type="file"></code> element within a form,
and then accessing selected files.
<pre class="lang-javascript">
// uploadData is a form element
// fileChooser is input element of type 'file'
var file = document.forms['uploadData']['fileChooser'].files[0];
// alternative syntax can be
// var file = document.forms['uploadData']['fileChooser'].files.item(0);
if(file)
{
// Perform file ops
}
</pre>
</div>
<h3 id="attributes-filelist">
Attributes</h3>
<dl>
<dt><dfn attribute for=FileList id="dfn-length">length</dfn>
<dd>must return the number of files in the {{FileList}} object.
If there are no files, this attribute must return 0.
</dl>
<h3 id="filelist-methods-params">
Methods and Parameters</h3>
<dl>
<dt><dfn method for=FileList id="dfn-item">item(index)</dfn>
<dd>must return the |index|th {{File}} object in the {{FileList}}.
If there is no |index|th {{File}} object in the {{FileList}},
then this method must return <code>null</code>.
<dfn argument for="FileList/item(index)" id="dfn-index">index</dfn> must be treated by user agents
as value for the position of a {{File}} object in the {{FileList}},
with 0 representing the first file.
<a>Supported property indices</a> are the numbers in the range zero
to one less than the number of {{File}} objects represented by the {{FileList}} object.
If there are no such {{File}} objects,
then there are no supported property indices.
</dl>
Note: The {{HTMLInputElement}} interface has a readonly attribute of type {{FileList}},
which is what is being accessed in the above example.
Other interfaces with a readonly attribute of type {{FileList}} include the {{DataTransfer}} interface.
<h2 id="reading-data-section">
Reading Data</h2>
<h3 id="readOperationSection">
The Read Operation</h3>
The algorithm below defines a <a>read operation</a>,
which takes a {{Blob}} and a <a>synchronous flag</a> as input,
and reads <a>byte</a>s into a byte stream
which is returned as the |result| of the <a>read operation</a>,
or else fails along with a <a>failure reason</a>.
Methods in this specification invoke the <a>read operation</a>
with the <a>synchronous flag</a> either set or unset.
The <dfn id="synchronousFlag">synchronous flag</dfn> determines if a read operation is synchronous or asynchronous,
and is *unset* by default.
Methods may set it.
If it is set,
the <a>read operation</a> takes place synchronously.
Otherwise, it takes place asynchronously.
To perform a <dfn id="readOperation">read operation</dfn> on a {{Blob}} and the <a>synchronous flag</a>,
run the following steps:
1. Let |s| be a a new [=/body=],
|b| be the {{Blob}} to be read from,
and |bytes| initially set to an empty byte sequence.
Set the |length| on |s| to the {{Blob/size}} of |b|.
While there are still bytes to be read in |b|,
perform the following substeps:
Note: The algorithm assumes that invoking methods have checked for <a>readability state</a>.
A {{Blob}} in the <a for="Blob/readability state"><code>CLOSED</code></a> state must not have a <a>read operation</a> called on it.
1. If the <a>synchronous flag</a> is set, follow the steps below:
1. Let |bytes| be the byte sequence that results from reading a <a>chunk</a> from |b|.
If a <a>file read error</a> occurs reading a <a>chunk</a> from |b|,
return |s| with the error flag set,
along with a <a>failure reason</a>,
and <a>terminate this algorithm</a>.
Note: Along with returning failure,
the synchronous part of this algorithm must return the <a>failure reason</a> that occurred
for <a lt="throw">throwing an exception</a> by synchronous methods
that invoke this algorithm with the <a>synchronous flag</a> set.
2. If there are no errors,
push |bytes| to |s|,
and increment |s|'s |transmitted| [[Fetch]]
by the number of bytes in |bytes|.
Reset |bytes| to the empty byte sequence
and continue reading <a>chunk</a>s as above.
3. When all the bytes of |b| have been read into |s|,
return |s|
and <a>terminate this algorithm</a>.
2. Otherwise, the <a>synchronous flag</a> is unset.
Return |s| and process the rest of this algorithm asynchronously.
3. Let |bytes| be the byte sequence that results from reading a <a>chunk</a> from |b|.
If a <a>file read error</a> occurs reading a <a>chunk</a> from |b|,
set the error flag on |s|,
and <a>terminate this algorithm</a> with a <a>failure reason</a>.
Note: The asynchronous part of this algorithm must signal the <a>failure reason</a> that occurred
for asynchronous error reporting by methods expecting |s|
and which invoke this algorithm with the <a>synchronous flag</a> unset.
4. If no <a>file read error</a> occurs,
push |bytes| to |s|,
and increment |s|'s |transmitted| [[Fetch]]
by the number of bytes in |bytes|.
Reset |bytes| to the empty byte sequence
and continue reading <a>chunk</a>s as above.
To perform an <dfn id="task-read-operation">annotated task read operation</dfn>
on a {{Blob}} |b|,
perform the steps below:
1. Perform a <a>read operation</a> on |b| with the <a>synchronous flag</a> unset,
along with the additional steps below.
2. If the <a>read operation</a> terminates with a <a>failure reason</a>,
<a>queue a task</a> to <dfn id="process-read-error">process read error</dfn> with the <a>failure reason</a>
and terminate this algorithm.
3. When the first <a>chunk</a> is being pushed to the [=/body=] |s| during the <a>read operation</a>,
<a>queue a task</a> to <dfn id="process-read">process read</dfn>.
4. Once the [=/body=] |s| from the <a>read operation</a> has at least one <a>chunk</a> read into it,
or there are no <a>chunk</a>s left to read from |b|,
<a>queue a task</a> to <dfn id="process-read-data">process read data</dfn>.
Keep <a lt="queue a task">queuing tasks</a> to <a>process read data</a>
for every <a>chunk</a> read or every 50ms,
whichever is *least frequent*.
5. When all of the <a>chunk</a>s from |b| are read into the [=/body=] |s| from the <a>read operation</a>,
<a>queue a task</a> to <dfn id="process-read-EOF">process read EOF</dfn>.
Use the <a>file reading task source</a> for all these tasks.
<h3 id="blobreader-task-source">
The File Reading Task Source</h3>
This specification defines a new generic <a>task source</a> called the <dfn id="fileReadingTaskSource">file reading task source</dfn>,
which is used for all <a lt="queue a task">tasks that are queued</a> in this specification
to read byte sequences associated with {{Blob}} and {{File}} objects.
It is to be used for features that trigger in response to asynchronously reading binary data.
<h3 id="APIASynch">
The FileReader API</h3>
<pre class="idl">
[Constructor, Exposed=(Window,Worker)]
interface FileReader: EventTarget {
// async read methods
void readAsArrayBuffer(Blob blob);
void readAsBinaryString(Blob blob);
void readAsText(Blob blob, optional DOMString label);
void readAsDataURL(Blob blob);
void abort();
// states
const unsigned short EMPTY = 0;
const unsigned short LOADING = 1;
const unsigned short DONE = 2;
readonly attribute unsigned short readyState;
// File or Blob data
readonly attribute (DOMString or ArrayBuffer)? result;
readonly attribute DOMException? error;
// event handler content attributes
attribute EventHandler onloadstart;
attribute EventHandler onprogress;
attribute EventHandler onload;
attribute EventHandler onabort;
attribute EventHandler onerror;
attribute EventHandler onloadend;
};
</pre>
<h4 id="filereaderConstrctr">
Constructor</h4>
When the {{FileReader()}} constructor is invoked,
the user agent must return a new {{FileReader}} object.
In environments where the global object is represented by a {{Window}} or a {{WorkerGlobalScope}} object,
the {{FileReader}} constructor must be available.
<h4 id="event-handler-attributes-section">
Event Handler Content Attributes</h4>
The following are the <a>event handler content attributes</a>
(and their corresponding <a>event handler event types</a>)
that user agents must support on {{FileReader}} as DOM attributes:
<table>
<thead>
<tr>
<th><a>event handler content attribute</a>
<th><a>event handler event type</a>
<tbody dfn-type=attribute dfn-for=FileReader>
<tr>
<td><dfn id="dfn-onloadstart">onloadstart</dfn>
<td>{{loadstart}}
<tr>
<td><dfn id="dfn-onprogress">onprogress</dfn>
<td>{{progress}}
<tr>
<td><dfn id="dfn-onabort">onabort</dfn>
<td>{{abort}}
<tr>
<td><dfn id="dfn-onerror">onerror</dfn>
<td>{{error!!event}}
<tr>
<td><dfn id="dfn-onload">onload</dfn>
<td>{{load}}
<tr>
<td><dfn id="dfn-onloadend">onloadend</dfn>
<td>{{loadend}}
</table>
<h4 id="blobreader-state">
FileReader States</h4>
The {{FileReader}} object can be in one of 3 states.
The <dfn attribute for=FileReader id="dfn-readyState">readyState</dfn> attribute,
on getting,
must return the current state,
which must be one of the following values:
<dl dfn-type=const dfn-for=FileReader>
<dt><dfn id="dfn-empty">EMPTY</dfn> (numeric value 0)
<dd>The {{FileReader}} object has been constructed,
and there are no pending reads.
None of the <a>read methods</a> have been called.
This is the default state of a newly minted {{FileReader}} object,
until one of the <a>read methods</a> have been called on it.
<dt><dfn id="dfn-loading">LOADING</dfn> (numeric value 1)
<dd>A {{File}} or {{Blob}} is being read.
One of the <a>read methods</a> is being processed,
and no error has occurred during the read.
<dt><dfn id="dfn-done">DONE</dfn> (numeric value 2)
<dd>The entire {{File}} or {{Blob}} has been read into memory,
OR a <a>file read error</a> occurred,
OR the read was aborted using {{FileReader/abort()}}.
The {{FileReader}} is no longer reading a {{File}} or {{Blob}}.
If {{FileReader/readyState}} is set to {{FileReader/DONE}}
it means at least one of the <a>read methods</a> have been called on this {{FileReader}}.
</dl>
<h4 id="reading-a-file">
Reading a File or Blob</h4>
The {{FileReader}} interface makes available several <dfn id="asynchronous-read-methods" lt="asynchronous read method">asynchronous read methods</dfn>--
{{FileReader/readAsArrayBuffer()}}, {{FileReader/readAsBinaryString()}}, {{FileReader/readAsText()}} and {{FileReader/readAsDataURL()}},
which read files into memory.
If multiple concurrent read methods are called on the same {{FileReader}} object,
user agents must throw an {{InvalidStateError}} on any of the read methods that occur
when {{FileReader/readyState}} = {{FileReader/LOADING}}.
({{FileReaderSync}} makes available several <a>synchronous read methods</a>.
Collectively, the sync and async read methods of {{FileReader}} and {{FileReaderSync}}
are referred to as just <dfn lt="read method">read methods</dfn>.)
<h5 id="filedata-attr">
The {{FileReader/result}} attribute</h5>
On getting, the <dfn attribute for=FileReader id="dfn-result">result</dfn> attribute returns a {{Blob}}'s data
as a {{DOMString}}, or as an {{ArrayBuffer}}, or <code>null</code>,
depending on the <a>read method</a> that has been called on the {{FileReader}},