FileSystemFileEntry.file()

This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

Non-standard
This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

The FileSystemFileEntry interface's method file() returns a File object which can be used to read data from the file represented by the directory entry.

Syntax

FileSystemFileEntry.file(successCallback[, errorCallback]);

Parameters

successCallback
A callback function which is called when the File has been created successfully; the File is passed into the callback as the only parameter.
errorCallback Optional
If provided, this must be a method which is called when an error occurs while trying to create the File. This callback receives as input a FileError object describing the error.

Editor's note: We need to find out what kinds of errors can occur and document them.

Return value

undefined.

Example

This example establishes a method, readFile(), reads a text file and calls a specified callback function with the received text (in a String object) once the read is completed. If an error occurs, a specified (optional) error callback is called.

function readFile(entry, successCallback, errorCallback) {
  entry.file(function(file) {
    let reader = new FileReader();

    reader.onload = function() {
      successCallback(reader.result);
    };

    reader.onerror = function() {
      errorCallback(reader.error);
    }

    reader.readAsText(file);
  }, errorCallback);
}

This function calls file(), specifying as its success callback a method which proceeds to use a FileReader to read the file as text. The FileReader's load event handler is set up to deliver the loaded string to the successCallback specified when the readFile() method was called; similarly, its error handler is set up to call the errorCallback specified.

Specifications

Specification Status Comment
File and Directory Entries API
The definition of 'file()' in that specification.
Draft Initial specification.

This API has no official W3C or WHATWG specification.

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic support
Non-standard
Chrome Full support 13Edge No support NoFirefox Full support 50IE No support NoOpera No support NoSafari No support NoWebView Android Full support YesChrome Android Full support YesEdge Mobile No support NoFirefox Android Full support 50Opera Android No support NoSafari iOS No support NoSamsung Internet Android ?

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
Non-standard. Expect poor cross-browser support.
Non-standard. Expect poor cross-browser support.

See also

Document Tags and Contributors

Contributors to this page: fscholz, cdl, kocoten1992, Sheppy
Last updated by: fscholz,