filesystem manager includes opening file dialog, csv manipulation etc.

filemanager.js

/**
 * File Manager for Chrome apps
 */
var fileManager = function() {

  /**
   * write a file using opendir dialog interactively.
   * @param {String} filename
   * @param {String} text to output into the file
   * @param {Function} callback(function(err, fileEntry){...}) Optional
   */
  function writeInteractively(filename, text, cb) {

    getFileEntryByOpenDir(filename, function(err, fileEntry) {
      if (chrome.runtime.lastError) {
        return cb && cb(chrome.runtime.lastError);
      }

      fileEntry.createWriter(function(fileWriter) {
        var truncated = false;
        var data = null;

        fileWriter.onwriteend = function(e) {
          fileWriter.onwriteend = null; // Avoid an infinite loop.
          // 余分なデータ尻をちょん切る。
          e.currentTarget.truncate(e.currentTarget.position);
          return cb && cb(null, fileEntry);
        };

        fileWriter.onerror = function(e) {
          return cb && cb(e);
        };

        data = new Blob([text], { type: 'text/plain' });
        fileWriter.write(data);

      }, function(e) {
        return cb && cb(e);
      });
    });

  }


  /**
   * read file using openfile dialog interactively.
   * @param {Function} callback(function(err, fileEntry){...})
   */
  function readInteractively(charset, cb) {
    getFileEntryByOpenFile(function(err, fileEntry) {
      if (chrome.runtime.lastError) {
        return cb && cb(chrome.runtime.lastError);
      }
      // Get a File object representing the file,
      // then use FileReader to read its contents.
      fileEntry.file(function(file) {
        let reader = new FileReader();

        reader.onloadend = function(e) {
          return cb && cb(null, this);
        };
        if (charset)
          reader.readAsText(file, charset);
        else
          reader.readAsText(file);
      }, function(e) {
        return cb && cb(e);
      });
    });
  }

  function getFileEntryByOpenDir(filename, cb) {
    let opts = { create: true }; // add "exclusive: true" to prevent overwrite

    chrome.fileSystem.chooseEntry({ 'type': "openDirectory" }, function(dirEntry) {
      if (!dirEntry) {
        return cb && cb("chooseEntry cancelled.");
      }
      dirEntry.getFile(
        filename, opts,
        function(fileEntry) {
          return cb && cb(null, fileEntry);
        },
        function(e) {
          return cb && cb(e);
        }
      );
    });
  }

  function getFileEntryByOpenFile(cb) {
    chrome.fileSystem.chooseEntry({ 'type': "openFile" }, function(fileEntry) {
      if (!fileEntry) {
        return cb && cb("chooseEntry cancelled.");
      }
      return cb && cb(null, fileEntry);
    });
  }

  function getDomInteractively(cb) {
    readInteractively(function(err, reader) {
      if (err) return cb && cb(err);
      let el = document.createElement('html');
      el.innerHTML = reader.result;
      return cb && cb(null, el);
    });
  }

  function parseCsvInteractively(charset, cb) {
    readInteractively(charset, function(err, fr) {
      console.log("err", err, "fr", fr);
      return cb(err, parseCsv(fr.result));
    });
  }

  function parseCsv(csvStr) {
    let rows = csvStr.split("\n");
    let len = rows.length;
    let row;
    let cols;
    let ret = [];
    for (let i = 0; i < len; i++) {
      row = rows[i];
      cols = row.split(",");
      ret.push(cols);
    }
    return ret;
  }

  //
  // -- public methods
  return {
    writeInteractively,
    readInteractively,
    getDomInteractively,
    parseCsvInteractively,
  };
}