Incorrect error handling when using nested try / catch blocks

Question

I have error handling set up using try/catch blocks, which in its simplified form looks like this

  try {
    // .. Some application logic

    try {
      // .. some async api code
    } catch (e) {
      throw new Error("Api Error")
    }

    return true;

  } catch (e) {
    throw new Error("Unknown Error")
  }

And the issue is, whenever I expect "Api Error" to be returned I get "Unknown Error" it seems like all errors are propagated to the outermost catch?

Is there a way to avoid this or another approach that allows for nested error handling?

Suhas NM · Accepted Answer · 2018-11-21 12:40:59Z

In your code, check if exception is happening inside the first try block. If so, the inner try won't be executed.

try {
    // .. Some application logic
    // exception occurs here
    // below code is not executed and the control is given to catch block
    try {
      //this did not execute
      // .. some async api code
    } catch (e) {
      throw new Error("Api Error")
    }

    return true;

  } 
  catch (e) {
    //control came here
    throw new Error("Unknown Error")
  }

This is also a possible case:

try {
    // .. Some application logic
    // no exceptions occur here
    // below code is executed
    try {
      //this did not execute
      //exception here
      // .. some async api code
    } catch (e) {
      //control came here and this threw APIerror
      throw new Error("Api Error")
    }
    //this did not execute as the previous catch block raised another exception
    return true;

  } 
  catch (e) {
    //control came here
    throw new Error("Unknown Error")
  }

Hope this helps :)

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