Debugging your application

Each application in JSAR is a standalone Node.js process, and each process will start a debugging server to provide the debugging interface for the developers. The debugging server is based on the Chrome DevTools Protocol, which allows developers to debug the application in the browser.

Prerequisites

Before you start debugging, you need to learn how to install adb tool and use logcat to view the console output.

Install adb

The adb tool is a command-line utility that allows you to communicate with an Android Open Source Project (AOSP) device. You can install the adb tool by following the instructions on the Android Developers website.

When you have installed the adb tool, you can use the following command to connect to the device via network:

adb connect <device-ip>

View the console output

JSAR outputs the console messages to the Android logcat, you can use the following command to view the console output:

adb logcat -s jsar

Then you can see the console output in the terminal:

07-12 22:12:23.326  9826  9850 D jsar    : client(9957): Detected a long frame(#135) takes 341ms in session(2)

Other logcat channels

There are other log channels used by JSAR, you can listen to them on-demand: adb logcat -s jsar -s jsar.error, the following table lists the log channels:

Channel	Description
jsar	The main log channel for JSAR
jsar.error	The error log channel for JSAR
TR_GLES	The OpenGL ES log channel

Looking for the debugging server

When you start the application, you will see the following message in the console:

07-12 22:14:34.649 10055 10075 D jsar    : client(10142): Debugger listening on ws://0.0.0.0:9229/6f969656-e8a2-4e93-a904-c9e1fe940c13

You can extract the debugging server port from the message, in this case, the port is 9229.

adb forward tcp:9229 tcp:9229

The above command forwards the port 9229 from the device to the host, then you can open the Chrome browser and navigate to chrome://inspect to connect to the debugging server.