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Debug
Debug
Debugging NativeScript for Android
1

Overview

Since NativeScript for Android embeds a JavaScript virtual machine (namely Google's V8) to process the JavaScript code, it also takes advantage of the debugger tools available for this virtual machine. These are Node Inspector and Chrome Developer Tools.

The article assumes that you are familiar with JavaScript debugging in the Chrome Developer Tools. The required node-inspector package is installed by the CLI. You will also need the Chrome web browser installed locally.

The current implementation supports two major scenarios:

  • Start debugging - starts an application with the debugger enabled
  • Attach/Detach debugger - attach/detach the debugger to a running application

Start an application with the debugger attached

The following command will build, deploy and run the application with the debugger attached:

tns debug android --debug-brk

Behind the scenes the debug command, together with the --debug-brk option, will build and start the application and then it will find an available port and enable V8's debugger on that port. Finally, it will start Node Inspector and launch Chrome browser.

Image1

In this case the debugger will automatically break at the first JavaScript statement.

Setting breakpoints in JavaScript

The global debugger statement causes V8 to stop program execution and start a debugging session at the line where it was called. It is equivalent to setting a "manual" breakpoint in the Sources tab of Chrome DevTools.

See this article for more information.

Attach the debugger

If you have a running application you can attach the debugger with the following command:

tns debug android --start

As in the previous scenario, the debug command will configure the V8 debugger port, forward the port, start Node Inspector and launch Chrome browser. It will however will not automatically break and will only hit manually set breakpoints.

Detach the debugger

You can detach the debugger from an already debugged application using the following command:

tns debug android --stop

Miscellaneous

You can check whether a debugger is enabled with the following command:

tns debug android --get-port

It will return the current debugger port, 0 otherwise.

The current implementation has hard-coded 30 seconds timeout for establishing a connection between the command line tool and the device/emulator.

See Also