lib/Ext/device/filesystem/HTML5.js
function(config) {
                if (config.offset == null) {
                    Ext.Logger.error('Ext.device.filesystem.FileEntry#seek: You must specify an `offset` in the file.');
                    return null;
                }

                this.offset = config.offset || 0;

                if (config.success) {
                    config.success.call(config.scope || this);
                }
            }
function(config) {
                if (config.offset == null) {
                    Ext.Logger.error('Ext.device.filesystem.FileEntry#seek: You must specify an `offset` in the file.');
                    return null;
                }

                this.offset = config.offset || 0;

                if (config.success) {
                    config.success.call(config.scope || this);
                }
            }
Sets the byte offset into the file at which the next read/write will occur.

@param {Object} config
The object which contains the following config options:

@param {Number} config.offset This is required.
The file offset to set. If negative, the offset back from the end of the file.

@param {Function} config.success This is optional.
The callback to be called when the file offset has been successfully set.

@param {Function} config.failure This is optional.
The callback to be called when an error occurred.

@param {Object} config.failure.error
The occurred error.

@param {Object} config.scope
The scope object