Error handling

Errors in NativeScript are handled differently to how they operate in a web app. By default when an unhandled exception is thrown in NativeScript, the app may crash, and an error with the corresponding stack trace will be shown. When the app is in development mode this may be the desired behaviour. However, when the app is in production an app crash can seriously hurt an app's credibility and drive away customers. In many cases, you'll want different error handling behavior between development and production (e.g. app freeze, blank screen, failed navigation).

NativeScript allows error handling to be set dependent on whether the app is in Development or Production mode in the following three ways:

Development Mode ​

Allow app crash: Throw exceptions as soon as an error occurs and crash the app.

const errorHandler: TraceErrorHandler = {
  handlerError(err) {
    throw err
  },
}

Prevent app crash: Write the error message to the console and continue the execution of the app.

const errorHandler: TraceErrorHandler = {
  handlerError(err) {
    Trace.write(err, 'unhandled-error', type.error)
  },
}

Production Mode ​

Prevent app crash: For example, send an error report to an analytics server but continue app execution.

const errorHandler: TraceErrorHandler = {
  handlerError(err) {
    reportToAnalytics(err)
  },
}

For more details about the TraceErrorHandler, see the Tracing in NativeScript page.

Disabling rethrowing of uncaught JS exceptions to native ​

Nativescript also allows the prevention of an app crash by disabling rethrowing of uncaught JS exceptions to native. This can be done by setting the discardUncaughtJsExceptions property to true inside the nativescript.config.ts file.

ios: {
...
    "discardUncaughtJsExceptions": true,

},
android: {
...
    "discardUncaughtJsExceptions": true,

},

To handle discarded exceptions, two options are available:

• Listening to the Application.discardedErrorEvent and using the received DiscardedErrorEventData instance

import { Application, DiscardedErrorEventData } from '@nativescript/core'

Application.on(
  Application.discardedErrorEvent,
  function (args: DiscardedErrorEventData) {
    const error = args.error

    console.log('Received discarded exception: ')
    console.log(error.message)
    console.log(error.name)
    console.log(error.stack)
    console.log(error.nativeError)
    // for example, report the exception to an analytics solution here
  }
)

• Assigning a one-argument function to global.__onDiscardedError which will receive the exception as a NativeScriptError instance.