Custom Error Class as a Node module to send custom error response

Question

Here I created Custom Error class in Node.js. I created this ErrorClass to send Custom error response of api call.

I want to catch this CustomError class in Bluebird Catch promises.

Object.defineProperty(Error.prototype, 'message', {
    configurable: true,
    enumerable: true
});

Object.defineProperty(Error.prototype, 'stack', {
    configurable: true,
    enumerable: true
});

Object.defineProperty(Error.prototype, 'toJSON', {
    value: function () {
        var alt = {};
        Object.getOwnPropertyNames(this).forEach(function (key) {
            alt[key] = this[key];
        }, this);

        return alt;
    },
    configurable: true
});

Object.defineProperty(Error.prototype, 'errCode', {
    configurable: true,
    enumerable: true
});

function CustomError(errcode, err, message) {
    Error.captureStackTrace(this, this.constructor);
    this.name = 'CustomError';
    this.message = message;
    this.errcode = errcode;
    this.err = err;
}

CustomError.prototype = Object.create(Error.prototype);

I wanna convert this into node-module but I am not getting how to do that.

Why are you adding message, stack and toJSON to Error.prototype? Why not just set them in CustomError? — thefourtheye
– thefourtheye, Commented Apr 21, 2015 at 15:20
@thefourtheye why define message/stack at all, they are already being inherited from Error.prototype. — James
– James, Commented Apr 21, 2015 at 15:24
@James Ah, I see why OP does that. He is making everything enumerable. — thefourtheye
– thefourtheye, Commented Apr 21, 2015 at 15:30
@thefourtheye ah, so they are. To be honest I only scanned the actual implementation as that wasn't really relevant to the question being asked. — James
– James, Commented Apr 21, 2015 at 15:41

Community · Accepted Answer · 2020-06-20 09:12:55Z

I want to catch this CustomError class in Bluebird Catch promises.

Quoting bluebird's documentation,

For a parameter to be considered a type of error that you want to filter, you need the constructor to have its .prototype property be instanceof Error.

Such a constructor can be minimally created like so:
function MyCustomError() {}
MyCustomError.prototype = Object.create(Error.prototype);
Using it:
Promise.resolve().then(function() {
    throw new MyCustomError();
}).catch(MyCustomError, function(e) {
    //will end up here now
});

So, you can catch the custom error object, like this

Promise.resolve().then(function() {
    throw new CustomError();
}).catch(CustomError, function(e) {
    //will end up here now
});

I wanna convert this into node-module but I am not getting how to do that.

You just have to assign whatever you want to export as part of the module, to module.exports. In this case, most likely, you might want to export the CustomError function and it can be done like this

module.exports = CustomError;

Read more about module.exports in this question, What is the purpose of Node.js module.exports and how do you use it?

James · Accepted Answer · 2015-04-21 15:21:13Z

1

A node module is nothing more than an exported class. In your example, if you export your CustomError class i.e.

module.exports = CustomError;

Then you would be able to import the module from another class

var CustomError = require("./CustomError");
...
throw new CustomError();

answered Apr 21, 2015 at 15:21

James

82.4k19 gold badges173 silver badges245 bronze badges

Collectives™ on Stack Overflow

Custom Error Class as a Node module to send custom error response

2 Answers 2

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related