How to use the node-ios-device.log function in node-ios-device

process.nextTick(function () {
		try {
			logOff = iosDevice.log(udid, function (msg) {
				if (state == PUMPING_LOG) {
					// we create a timer here so that if we haven't received any messages for a
					// half second, then the log must be caught up and we're ready to install
					clearTimeout(timer);
					timer = setTimeout(function () {
						// logs quieted down, go ahead and install
						state = INSTALLING;
						iosDevice.installApp(udid, appPath, function (err) {
							if (err) {
								emitter.emit('error', err);
								trackOff();
								logOff && logOff();
							} else {
								emitter.emit('installed');
							}
							callback(err);

iosDevice.installApp(udid, appPath, function (err) {
			if (err) {
				return handle.emit('error', err);
			}

			handle.emit('installed');

			if (options.logPort) {
				var logHandle = iosDevice
					.log(udid, options.logPort)
					.on('log', function (msg) {
						handle.emit('log', msg);
					})
					.on('app-started', function () {
						handle.emit('app-started');
					})
					.on('app-quit', function () {
						handle.emit('app-quit');
					})
					.on('disconnect', function () {
						handle.emit('disconnect');
					})
					.on('error', function (err) {
						handle.emit('log-error', err);
					});