Can I throw an anonymous object in JavaScript?

Question

Mozilla says that we can define an object and throw it.

This way, we can encapsulate more than a simple string message and send it to the exception consumer (the catch block, or the then method of promises).

However, I don't want to constantly define types in my JS code.

Is it possible to throw anonymous objects?

I tried throw new Error({ firstKey: firstValue, secondKey: secondValue }) and it does not work. I get [object Object].

That works fine, it just means that somewhere in your code, you're turning it into a string instead of looking at the object properties. — CertainPerformance, Nov 24 '22 at 15:28
Your object needs a `toString` function for your example to work. Like `throw new Error({firstKey: 1, secondKey: 2, toString: () => 123})`. — Lain, Nov 24 '22 at 15:30
try `throw { firstKey: firstValue, secondKey: secondValue }` directly — R4ncid, Nov 24 '22 at 15:30
@R4ncid An Error object is usually a bit nicer to work with: https://eslint.org/docs/latest/rules/no-throw-literal — CertainPerformance, Nov 24 '22 at 15:31
@CertainPerformance, simply open a browser window, open the dev tools, then write `throw new Error({name: 'somebody, age: 40})`. You see `[object Object]` and nowhere you have turned it into string. — Big boy, Nov 27 '22 at 11:54
@Lain, I added that `toString` method and now I recieve the return value of that method. That's not what I want. I want to get the object. — Big boy, Nov 27 '22 at 12:31

score 2 · Answer 1 · answered Nov 27 '22 at 14:55

When an Error is created, the first parameter passed (if any) is converted to a string, and not used anywhere else. So, just by using the first parameter, there's no way to pass an object along (without using JSON.stringify, which would be ugly and also lose information).

But Errors can accept a second argument - an object with a cause property, which will then get put on the error object. You can use this to communicate any information you want, including objects.

const objForCause = {};
try {
  throw new Error(
    'Something went wrong',
    { cause: { prop: 'val', obj: objForCause } }
  );
} catch(err) {
  // Not all errors have causes
  // Ensure that it does before examining further
  if (err.cause) {
    console.log(err.cause);
    console.log(err.cause.obj === objForCause);
  }
}

Marco · Accepted Answer · 2022-11-27T15:07:42.667

1

In javascript, you can throw literally anything:

try {
  throw "a string";
} catch (error) {
  console.log("caught", error)
}

try {
  throw 10;
} catch (error) {
  console.log("caught", error)
}

try {
  throw {a: 1, b: 2};
} catch (error) {
  console.log("caught", error)
}

So to answer the question Is it possible to throw anonymous objects?: yes it's possible to throw an anonymous object.

Whether you should do so is another question.

edited Nov 27 '22 at 15:07

answered Nov 27 '22 at 15:02

Marco

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You saved my life. Thank you so much. No complexity. Jus throw an object. And it worked like a charm. – Big boy Nov 28 '22 at 02:40
@Bigboy Glad to be of help. No problem! – Marco Nov 28 '22 at 13:33

score 0 · Answer 3 · answered Nov 27 '22 at 15:27

If you read your own question statement carefully. This is what is being said.

Define your own object

  const myobj={a:1,b:2};

Then throw it.

  throw myobj;

Use the object however you want

console.log(err);

Below is a working example.

try {
  const myobj = {
    a: 1,
    b: 2
  };
  throw myobj;
} catch (err) {
  console.log(err);
}

You can do all sorts of things depending upon your imagination I guess. even attaching a error object instance if you want.

Can I throw an anonymous object in JavaScript?

3 Answers3