Revision 487155 of FileReader

  • Revision slug: Web/API/FileReader
  • Revision title: FileReader
  • Revision id: 487155
  • Created:
  • Creator: gordonwoodhull
  • Is current revision? No
  • Comment grammar

Revision Content

{{ MultiRef({"apis": ["Blob","File","FileList","FileReader"]}) }}

Summary

The FileReader object lets web applications asynchronously read the contents of files (or raw data buffers) stored on the user's computer, using {{ domxref("File") }} or {{ domxref("Blob") }} objects to specify the file or data to read.

File objects may be obtained from a {{ domxref("FileList") }} object returned as a result of a user selecting files using the {{ HTMLElement("input") }} element, from a drag and drop operation's DataTransfer object, or from the mozGetAsFile() API on an {{ domxref("HTMLCanvasElement") }}.

Constructor

FileReader FileReader();

See Using files from web applications for details and examples.

Properties

{{domxref("FileReader.error")}} {{readonlyinline}}
A {{domxref("DOMError")}} representing the error that occurred while reading the file.
{{domxref("FileReader.readyState")}} {{readonlyinline}}
A number indicating the state of the FileReader. This will be one of the {{ anch("State constants") }}.
{{domxref("FileReader.result")}} {{readonlyinline}}
The file's contents. This property is only valid after the read operation is complete, and the format of the data depends on which of the methods was used to initiate the read operation.

Event handlers

{{domxref("FileReader.onabort")}}
A handler for the {{event("abort")}} event. This event is triggered each time the reading operation is aborted.
{{domxref("FileReader.onerror")}}
A handler for the {{event("error")}} event. This event is triggered each time the reading operation encounter an error.
{{domxref("FileReader.onload")}}
A handler for the {{event("load")}} event. This event is triggered each time the reading operation is successfully completed.
{{domxref("FileReader.onloadstart")}}
A handler for the {{event("loadstart")}} event. This event is triggered each time the reading is starting.
{{domxref("FileReader.onloadend")}}
A handler for the {{event("loadend")}} event. This event is triggered each time the reading operation is completed (either in success or failure).
{{domxref("FileReader.onprogress")}}
A handler for the {{event("progress")}} event. This event is triggered while reading a {{domxref("Blob")}} content.

Note: As FileReader inherit from {{domxref("EventTarget")}}, all those events can also be listen by using the {{domxref("EventTarget.addEventListener()","addEventListener")}} method.

State constants

  • EMPTY   : 0 : No data has been loaded yet.
  • LOADING : 1 : Data is currently being loaded.
  • DONE    : 2 : The entire read request has been completed.

Methods

{{domxref("FileReader.abort()")}}
Aborts the read operation. Upon return, the readyState will be DONE.
{{domxref("FileReader.readAsArrayBuffer()")}} {{ gecko_minversion_inline("7.0") }}
Starts reading the contents of the specified {{ domxref("Blob") }}, once finished, the result attribute contains an {{domxref("ArrayBuffer")}} representing the file's data.
{{domxref("FileReader.readAsBinaryString()")}}
Starts reading the contents of the specified {{ domxref("Blob") }}, once finished, the result attribute contains the raw binary data from the file as a string.
{{domxref("FileReader.readAsDataURL()")}}
Starts reading the contents of the specified {{ domxref("Blob") }}, once finished, the result attribute contains a data: URL representing the file's data.
{{domxref("FileReader.readAsText()")}}
Starts reading the contents of the specified {{ domxref("Blob") }}, once finished, the result attribute contains the contents of the file as a text string.

Specifications

Specification Status Comment
{{SpecName('File API','#FileReader-interface','FileReader')}} {{Spec2('File API')}} Initial definition.

Browser compatibility

{{ CompatibilityTable() }}

Feature Firefox (Gecko) Chrome Internet Explorer* Opera* Safari
Basic support {{ CompatGeckoDesktop("1.9.2") }} 7 10 12.02 6.0.2
Feature Firefox Mobile (Gecko) Android IE Mobile Opera Mobile Safari Mobile
Basic support {{ CompatUnknown() }} {{ CompatUnknown() }} {{ CompatUnknown() }} {{ CompatUnknown() }} {{ CompatUnknown() }}

Implementation notes

Gecko-specific notes

  • Prior to Gecko 2.0 beta 7 (Firefox 4.0 beta 7), all {{ domxref("Blob") }} parameters below were {{ domxref("File") }} parameters; this has since been updated to match the specification correctly.
  • Prior to Gecko 13.0 {{ geckoRelease("13.0") }} the FileReader.error property returned a {{ domxref("FileError") }} object. This interface has been removed and FileReader.error is now returning the {{ domxref("DOMError") }} object as defined in the latest FileAPI draft.

See also

Revision Source

<p>{{ MultiRef({"apis": ["Blob","File","FileList","FileReader"]}) }}</p>
<h2 id="Summary">Summary</h2>
<p>The <code>FileReader</code> object lets web applications asynchronously read the contents of files (or raw data buffers) stored on the user's computer, using {{ domxref("File") }} or {{ domxref("Blob") }} objects to specify the file or data to read.</p>
<p>File objects may be obtained from a {{ domxref("FileList") }} object returned as a result of a user selecting files using the {{ HTMLElement("input") }} element, from a drag and drop operation's <a href="/En/DragDrop/DataTransfer" title="En/DragDrop/DataTransfer"><code>DataTransfer</code></a> object, or from the <code>mozGetAsFile()</code> API on an&nbsp;{{ domxref("HTMLCanvasElement") }}.</p>
<h2 id="Constructor">Constructor</h2>
<pre class="syntaxbox">
FileReader FileReader();</pre>
<p>See <a href="/en/Using_files_from_web_applications" title="en/Using files from web applications">Using files from web applications</a> for details and examples.</p>
<h2 id="Properties" name="Properties">Properties</h2>
<dl>
 <dt>
  {{domxref("FileReader.error")}} {{readonlyinline}}</dt>
 <dd>
  A {{domxref("DOMError")}} representing the error that occurred while reading the file.</dd>
 <dt>
  {{domxref("FileReader.readyState")}} {{readonlyinline}}</dt>
 <dd>
  A number indicating the state of the <code>FileReader</code>. This will be one of the {{ anch("State constants") }}.</dd>
 <dt>
  {{domxref("FileReader.result")}} {{readonlyinline}}</dt>
 <dd>
  The file's contents. This property is only valid after the read operation is complete, and the format of the data depends on which of the methods was used to initiate the read operation.</dd>
</dl>
<h3 id="Events_Handler">Event handlers</h3>
<dl>
 <dt>
  {{domxref("FileReader.onabort")}}</dt>
 <dd>
  A handler for the {{event("abort")}} event. This event is triggered each time the reading operation is aborted.</dd>
 <dt>
  {{domxref("FileReader.onerror")}}</dt>
 <dd>
  A handler for the {{event("error")}} event. This event is triggered each time the reading operation encounter an error.</dd>
 <dt>
  {{domxref("FileReader.onload")}}</dt>
 <dd>
  A handler for the {{event("load")}} event. This event is triggered each time the reading operation is successfully completed.</dd>
 <dt>
  {{domxref("FileReader.onloadstart")}}</dt>
 <dd>
  A handler for the {{event("loadstart")}} event. This event is triggered each time the reading is starting.</dd>
 <dt>
  {{domxref("FileReader.onloadend")}}</dt>
 <dd>
  A handler for the {{event("loadend")}} event. This event is triggered each time the reading operation is completed (either in success or failure).</dd>
 <dt>
  {{domxref("FileReader.onprogress")}}</dt>
 <dd>
  A handler for the {{event("progress")}} event. This event is triggered while reading a {{domxref("Blob")}} content.</dd>
</dl>
<div class="note">
 <p>Note: As <code>FileReader</code> inherit from {{domxref("EventTarget")}}, all those events can also be listen by using the {{domxref("EventTarget.addEventListener()","addEventListener")}} method.</p>
</div>
<h3 id="State_constants" name="State_constants">State constants</h3>
<ul>
 <li><code>EMPTY &nbsp;</code> : <code>0</code> : No data has been loaded yet.</li>
 <li><code>LOADING</code> : <code>1</code> : Data is currently being loaded.</li>
 <li><code>DONE &nbsp;&nbsp;</code> : <code>2</code> : The entire read request has been completed.</li>
</ul>
<h2 id="Methods" name="Methods">Methods</h2>
<dl>
 <dt>
  {{domxref("FileReader.abort()")}}</dt>
 <dd>
  Aborts the read operation. Upon return, the <code>readyState</code> will be <code>DONE</code>.</dd>
 <dt>
  {{domxref("FileReader.readAsArrayBuffer()")}} {{ gecko_minversion_inline("7.0") }}</dt>
 <dd>
  Starts reading the contents of the specified {{ domxref("Blob") }}, once finished, the <code>result</code> attribute contains an {{domxref("ArrayBuffer")}} representing the file's data.</dd>
 <dt>
  {{domxref("FileReader.readAsBinaryString()")}}</dt>
 <dd>
  Starts reading the contents of the specified {{ domxref("Blob") }}, once finished, the <code>result</code> attribute contains the raw binary data from the file as a string.</dd>
 <dt>
  {{domxref("FileReader.readAsDataURL()")}}</dt>
 <dd>
  Starts reading the contents of the specified {{ domxref("Blob") }}, once finished, the <code>result</code> attribute contains a <code>data:</code> URL representing the file's data.</dd>
 <dt>
  {{domxref("FileReader.readAsText()")}}</dt>
 <dd>
  Starts reading the contents of the specified {{ domxref("Blob") }}, once finished, the <code>result</code> attribute contains the contents of the file as a text string.</dd>
</dl>
<h2 id="Specifications">Specifications</h2>
<table class="standard-table">
 <tbody>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
  <tr>
   <td>{{SpecName('File API','#FileReader-interface','FileReader')}}</td>
   <td>{{Spec2('File API')}}</td>
   <td>Initial definition.</td>
  </tr>
 </tbody>
</table>
<h2 id="Browser_compatibility" name="Browser_compatibility">Browser compatibility</h2>
<p>{{ CompatibilityTable() }}</p>
<div id="compat-desktop">
 <table class="compat-table">
  <tbody>
   <tr>
    <th>Feature</th>
    <th>Firefox (Gecko)</th>
    <th>Chrome</th>
    <th>Internet Explorer*</th>
    <th>Opera*</th>
    <th>Safari</th>
   </tr>
   <tr>
    <td>Basic support</td>
    <td>{{ CompatGeckoDesktop("1.9.2") }}</td>
    <td>7</td>
    <td>10</td>
    <td>12.02</td>
    <td>6.0.2</td>
   </tr>
  </tbody>
 </table>
</div>
<div id="compat-mobile">
 <table class="compat-table">
  <tbody>
   <tr>
    <th>Feature</th>
    <th>Firefox Mobile (Gecko)</th>
    <th>Android</th>
    <th>IE Mobile</th>
    <th>Opera Mobile</th>
    <th>Safari Mobile</th>
   </tr>
   <tr>
    <td>Basic support</td>
    <td>{{ CompatUnknown() }}</td>
    <td>{{ CompatUnknown() }}</td>
    <td>{{ CompatUnknown() }}</td>
    <td>{{ CompatUnknown() }}</td>
    <td>{{ CompatUnknown() }}</td>
   </tr>
  </tbody>
 </table>
</div>
<h3 id="Implementation_notes">Implementation notes</h3>
<ul>
 <li>IE9 has a <a href="http://html5labs.interoperabilitybridges.com/prototypes/fileapi/fileapi/info" title="http://html5labs.interoperabilitybridges.com/prototypes/fileapi/fileapi/info">File API Lab</a>.</li>
 <li>Opera has <a href="http://www.opera.com/docs/specs/presto28/file/" title="http://my.opera.com/desktopteam/blog/2011/04/05/stability-gmail-socks">partial support</a> in 11.1.</li>
</ul>
<h4 id="Gecko-specific_notes">Gecko-specific notes</h4>
<ul>
 <li>Prior to Gecko 2.0 beta 7 (Firefox 4.0 beta 7), all {{ domxref("Blob") }} parameters below were {{ domxref("File") }} parameters; this has since been updated to match the specification correctly.</li>
 <li>Prior to Gecko 13.0 {{ geckoRelease("13.0") }} the <code>FileReader.error</code> property returned a {{ domxref("FileError") }} object. This interface has been removed and <code>FileReader.error</code> is now returning the {{ domxref("DOMError") }} object as defined in the latest FileAPI draft.</li>
</ul>
<h2 id="See_also" name="See_also">See also</h2>
<ul>
 <li><a href="/en/Using_files_from_web_applications" title="en/Using files from web applications">Using files from web applications</a></li>
 <li>{{ domxref("File") }}</li>
 <li>{{ domxref("Blob") }}</li>
</ul>
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