FileWriter

As object that allows you to create and write data to a file.

Properties

  • readyState: One of the three possible states, either INIT, WRITING, or DONE.

  • fileName: The name of the file to be written. (DOMString)

  • length: The length of the file to be written. (long)

  • position: The current position of the file pointer. (long)

  • error: An object containing errors. (FileError)

  • onwritestart: Called when the write starts. (Function)

  • onwrite: Called when the request has completed successfully. (Function)

  • onabort: Called when the write has been aborted. For instance, by invoking the abort() method. (Function)

  • onerror: Called when the write has failed. (Function)

  • onwriteend: Called when the request has completed (either in success or failure). (Function)

The following property is not supported:

  • onprogress: Called while writing the file, reporting progress in terms of progress.loaded/progress.total. (Function)

    Methods

  • abort: Aborts writing the file.

  • seek: Moves the file pointer to the specified byte.

  • truncate: Shortens the file to the specified length.

  • write: Writes data to the file.

Details

The FileWriter object offers a way to write UTF-8 encoded files to the device file system. Applications respond to writestart, progress, write, writeend, error, and abort events.

Each FileWriter corresponds to a single file, to which data can be written many times. The FileWriter maintains the file's position and length attributes, which allow the app to seek and write anywhere in the file. By default, the FileWriter writes to the beginning of the file, overwriting existing data. Set the optional append boolean to true in the FileWriter's constructor to write to the end of the file.

Text data is supported by all platforms listed below. Text is encoded as UTF-8 before being written to the filesystem. Some platforms also support binary data, which can be passed in as either an ArrayBuffer or a Blob.

Supported Platforms

Text and Binary Support:

  • Amazon Fire OS
  • Android
  • iOS

Text-only Support:

  • BlackBerry WebWorks 5.0+
  • Windows Phone 7 and 8
  • Windows 8

Seek Quick Example

function win(writer) {
    // fast forwards file pointer to end of file
    writer.seek(writer.length);
};

var fail = function(evt) {
    console.log(error.code);
};

entry.createWriter(win, fail);

Truncate Quick Example

function win(writer) {
    writer.truncate(10);
};

var fail = function(evt) {
    console.log(error.code);
};

entry.createWriter(win, fail);

Write Quick Example

function win(writer) {
    writer.onwrite = function(evt) {
        console.log("write success");
    };
    writer.write("some sample text");
};

var fail = function(evt) {
    console.log(error.code);
};

entry.createWriter(win, fail);

Binary Write Quick Example

function win(writer) {
    var data = new ArrayBuffer(5),
        dataView = new Int8Array(data);
    for (i=0; i < 5; i++) {
        dataView[i] = i;
    }
    writer.onwrite = function(evt) {
        console.log("write success");
    };
    writer.write(data);
};

var fail = function(evt) {
    console.log(error.code);
};

entry.createWriter(win, fail);

Append Quick Example

function win(writer) {
    writer.onwrite = function(evt) {
    console.log("write success");
};
writer.seek(writer.length);
    writer.write("appended text");
};

var fail = function(evt) {
    console.log(error.code);
};

entry.createWriter(win, fail);

Abort Quick Example

function win(writer) {
    writer.onwrite = function(evt) {
        console.log("write success");
    };
    writer.write("some sample text");
    writer.abort();
};

var fail = function(evt) {
    console.log(error.code);
};

entry.createWriter(win, fail);

Full Example

<!DOCTYPE html>
<html>
  <head>
    <title>FileWriter Example</title>

    <script type="text/javascript" charset="utf-8" src="cordova.js"></script>
    <script type="text/javascript" charset="utf-8">

    // Wait for device API libraries to load
    //
    document.addEventListener("deviceready", onDeviceReady, false);

    // device APIs are available
    //
    function onDeviceReady() {
        window.requestFileSystem(LocalFileSystem.PERSISTENT, 0, gotFS, fail);
    }

    function gotFS(fileSystem) {
        fileSystem.root.getFile("readme.txt", {create: true, exclusive: false}, gotFileEntry, fail);
    }

    function gotFileEntry(fileEntry) {
        fileEntry.createWriter(gotFileWriter, fail);
    }

    function gotFileWriter(writer) {
        writer.onwriteend = function(evt) {
            console.log("contents of file now 'some sample text'");
            writer.truncate(11);
            writer.onwriteend = function(evt) {
                console.log("contents of file now 'some sample'");
                writer.seek(4);
                writer.write(" different text");
                writer.onwriteend = function(evt){
                    console.log("contents of file now 'some different text'");
                }
            };
        };
        writer.write("some sample text");
    }

    function fail(error) {
        console.log(error.code);
    }

    </script>
  </head>
  <body>
    <h1>Example</h1>
    <p>Write File</p>
  </body>
</html>