Error breaking out of a try/catch statement

July 30, 2023

As i was programming a NPM package, i came to need of a try{}catch{} statement, but error sometimes breaks out of try{} part and terminates the entire process.

As try{}catch{} is used to catch errors from try{} part and handle them with the catch{} part, I expected that the error will be caught and passed to catch{}, but when a function returns an error using return, not throw statement, the error breaks out. I tried different call methods, such as .call(...) or .apply(...), but the problem persists.

This passes:

let result;

let throwError = () => throw new Error("I didn't break out!");

try {
  let res = throwError();
  result = res;
} catch(err) {
  result = {
    message: err.message,
    name: err.name
  }
}

result; // {name: "Error", message: "I didn't break out!"}

This fails:

let result;

let returnError = () => new Error("I broke out!")

try {
  let res = returnError(); // Error: I broke out!
  result = res;
} catch(err) {
  result = {
    message: err.message,
    name: err.name
  }
}

>Solution :

There’s no problem here. If you want to catch an error being throw, try/catch will do that. If you want to catch an error being returned, you need a different check for that.

let result;

let returnError = () => new Error("I broke out!")

try {
  let res = returnError();
  
  if (res instanceof Error) {
    throw res;
  }

  result = res;
} catch(err) {
  result = {
    message: err.message,
    name: err.name
  }
}