I am trying to create custom errors for better reporting on my API. I am using a custom class called ValidationError. I create a new object of this class and throw it in try block. Thus, the object now comes into the catch class.
try{
throw new ValidationError('Balance is insufficient')
}catch(err){
console.log(err instanceof ValidationError) // returns true
next(err)
}
So far everything is working fine. next(err) sends the control to this function in app.js
app.use((err , req , res , next)=>{
console.log(err , err instanceof ValidationError)
if(err instanceof ValidationError) return res.status(400).json({err : err.message})
res.status(500).json({err : "Something went wrong. Internal error"})
})
Here this is the result of the console.log :
ValidationError [SequelizeValidationError]: Balance is insufficient
at C:\Users\ganes\Documents\Software\DFinSerT\Tradilearn\backend\core\Routes\transactions.js:51:18
at processTicksAndRejections (node:internal/process/task_queues:96:5) {
errors: []
} false
As you can see, err has the same message so, I assume, it is the same object, but now it is no more an instance of ValidationError.
However, if I reject() an object of Validation error from a custom Promise, The control is not reaching the catch block of the route where the promise was called from. Instead it is directly going to the app.use error handler and this is the output.
ValidationError: Stock does not exists
at C:\Users\ganes\Documents\Software\DFinSerT\Tradilearn\backend\core\Utils\Validators\stocks.js:11:29
at processTicksAndRejections (node:internal/process/task_queues:96:5) true
This is the class definition
module.exports = class ValidationError extends Error {
constructor(message) {
super(message);
this.name = this.constructor.name;
Object.setPrototypeOf(this, ValidationError.prototype);
}
}
As you can see, when the validation error is created from a Promise, it does not lose the instance. But when called from catch block using next() it loses the instance. Can someone please explain this behaviour? Thanks.
