How to throw custom object as Error in Javascript

Question

I'm extending Error object here and passing the status code, code and the message.

class AuthenticationException extends Error {
constructor(statusCode, code, message) {
super();
this.statusCode = statusCode;
this.message = message;
this.code = code;
}
}
export default AuthenticationException;

But the Error throws only like below

{
"error": "Unable to decode token"
}

But this is not what i was looking for. The result should be like,

{
"message": "Unable to decode token",
"code":1234
}

Please help me If you can. And can I get many key-value pair as throw exception?

Dennis Hackethal · Accepted Answer · 2021-03-17 03:34:12Z

5

My guess is that the call to super() throws before the assignments run. But since super() needs to be called before accessing this, you may be out of luck.

Even if you could skip super(), you'd need to find a way of telling the Error class to print not only message but also code and statusCode.

What you're trying to do can be achieved by just throwing the object you need:

throw { message: '...', code: '...', statusCode: '...' }

Or, if you use this in a bunch of places and don't want to keep typing out the object, use a function:

let customThrow = (message, code, statusCode) => {
  throw { message, code, statusCode };
}

There's no need for classes, let alone inheritance. Much simpler this way.

edited Mar 17, 2021 at 3:34

answered Mar 17, 2021 at 3:24

Dennis Hackethal

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5 Comments

ahkam Over a year ago

Appreciate your answer. Are there any other ways where I can throw an error like a JSON object?

ahkam Over a year ago

This object will be in the console right?. But I want to get it to the window as a json response

Dennis Hackethal Over a year ago

Yes. What do you mean by "to the window"?

ahkam Over a year ago

I got it buddy. Thanks:)

Dennis Hackethal Over a year ago

Ok but can you still explain what you meant so I know?

Sang · Accepted Answer · 2023-02-16 06:50:00Z

You can't throw an object as an error. The Error constructor doesn't support that. Another approach is to have the custom object in a separate property. You can get that custom object out in the catch block:

export type ApiError = {
  statusCode: number;
  code: number;
};

export class AuthenticationException extends Error {
  public apiError: ApiError;

  constructor(message: string, apiError: ApiError, options?: ErrorOptions) {
    super(message, options);

    this.apiError = apiError;
    this.message = message;
  }
}

try {
  throw new AuthenticationException('Unable to decode token', {
    code: 1234,
    statusCode: 401,
  });
} catch (e) {
  if (e instanceof AuthenticationException) {
    console.log(e.message);
    console.log(e.apiError);
  }
}

Console output:

Unable to decode token
{
  "code": 1234,
  "statusCode": 401
}

Reference:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error#custom_error_types

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