While using app.useGlobalFilters(new MongoExceptionFilter()); in main.ts in a NestJS app (or a local controller MongoExceptionFilter), the MongoException is not getting caught whenever I call an async function without await -- it just crashes the NestJS app with a MongoException

async funcA
   await funcB // works well, MongoExceptionFilter does its job
   funcB       // crashes the app, why doesn't MongoExceptionFilter catch this?

async funcB
  //  throws a MongoException

tried to call the func with await - it worked but wouldn't work without await

CodePudding user response：

If you don't await an asynchronous function, the promise is unhandled and the method is considered to be called synchronously. Because of this, the response can be sent to the client ending the lifecycle of the request and Nest's try/catch around anything that happens within the request. Think of it as an express middleware. Essentially, you've called the next callback without indicating there's an error, and then an error happens later on. Because the execution stack has already moved on it's impossible for the error handler to know to listen for that exception