chrome/chromium app: read RFID cards via chome.serial

rfidReader = {
    webview: null,
    connectionId: '',
    connected: false,
    infoInterval: null,
    stringReceived: '',
 
    /**
     * Initialize the rfid reader connection and register the onReceive event
     *
     * @return void
     */
    init: function() {
        var self = this;
 
        window.addEventListener('load', function() {
            self.webview = document.getElementById('guestportalWebview');
 
            self.webview.addEventListener("loadstop", function() {
                if (self.connected) {
                    return;
                }
 
                // load all devices
                chrome.serial.getDevices(self.getDevicesCallback);
                chrome.serial.onReceive.addListener(self.onReceiveCallback);
            });
        });
    },
 
    /**
     * Convert an array buffer into a string.
     *
     * @param array data
     *
     * @return String
     */
    convertArrayBufferToString: function (data) {
        return String.fromCharCode.apply(null, new Uint8Array(data));
    },
 
    /**
     * Removes not used numbers from the serial readout and trim it.
     * This has to be done, otherwise the card id is not usable.
     *
     * Example:
     * 39383431303030313131333036393032 converts to 9841000111306902
     *
     * @param String result
     *
     * @return String
     */
    convertResult: function(result) {
        return result.replace(/\d(\d)/g, '$1').replace(/^\s+|\s+$/gm, '');
    },
 
    /**
     * The callback for fetching the available serial devices.
     *
     * @param array ports Array of XXX with all available devices
     *
     * @return void
     */
    getDevicesCallback: function(ports) {
        var path = null;
 
        if (typeof ports === 'undefined') {
            rfidReader.showError('No serial devices found.');
            return;
        } else if  (ports.length === 0) {
            if (clientInformation.platform.match(/linux/i)) {
                //we do not get any information about serial devices
                // on linux, so we simply assume there is one
                path = '/dev/ttyS0';
            } else {
                rfidReader.showError('No serial devices found.');
                return;
            }
        } else {
            path = ports[0].path;
        }
 
        // connect to the first serial device
        chrome.serial.connect(path, {bitrate: 19200}, function(connectionInfo) {
            if (typeof connectionInfo === 'undefined') {
                rfidReader.showError('Cannot access serial device.');
                return;
            }
            rfidReader.connectionId = connectionInfo.connectionId;
            rfidReader.connected = true;
        });
    },
 
    /**
     * The callback for fetching the data sent by the serial reader.
     *
     * @param object info The readout from the serial port
     *
     * @return void
     */
    onReceiveCallback: function(info) {
        if (info.connectionId == rfidReader.connectionId && info.data) {
            var str = rfidReader.convertArrayBufferToString(info.data);
 
            if (str.charAt(str.length-1) === "\n") {
                rfidReader.stringReceived += str.substring(0, str.length-1);
                rfidReader.stringReceived = rfidReader.convertResult(rfidReader.stringReceived);
 
                if (rfidReader.stringReceived === '') {
                    console.log('received an empty string');
                    return;
                }
 
                // send the retreived data to the webview content
                rfidReader.webview.contentWindow.postMessage({cardId: rfidReader.stringReceived}, '*');
                rfidReader.stringReceived = '';
            } else {
                rfidReader.stringReceived += str;
            }
        }
    },
 
    showError: function(message) {
        console.error(message);
        document.getElementById('error').appendChild(document.createTextNode(message));
        document.getElementById('error').style.display = 'block';
    }
};
 
rfidReader.init();