FileSystemFileEntry.file() - Web APIs 编辑

Experimental

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

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

Browser compatibility

BCD tables only load in the browser

See also

• File and Directory Entries API
• Introduction to the File System API