Assert or type assert that error is an Error
npm install @poppanator/assert-errorWhen using strict errors in TS the type of the error in the catch clause
is unknown. This is a good thing since it forces you to properly handle the
error.
This package provides two functions to make this error handling easier.
The usual npm install @poppanator/assert-error,yarn add @poppanator/assert-error, etc...
Ponder the following
``ts`
try {
// Do some funky salsa
} catch (err: unknown) {
console.error('Error message:', err.message)
// .................................^^^^^^^
// It's a nono
}
Since TS doesn't know wether err is an error object or not you can't index
on it.
But using assertError() you can:
`ts
import { assertError } from '@poppanator/assert-error'
try {
// Do some funky chimichurri
} catch (err: unknown) {
assertError(err)
console.error('Error message:', err.message)
// It's a Yay-Yay
}
`
Now TS known ist's an Error object and indexing on it is fine.
If err is not an instance of (at least) Error, assertError() will throw.
To assert err is some other error than Error, you can provide the classassertError()
constructor as second argument to :
`ts
class MyError extends Error {
public code = 12
}
try {
// Do some funky pesto
} catch (err: unknown) {
assertError(err, MyError)
console.error('Error:', err.code)
}
`
Now, you may not always want something to throw in you catch clause. IfassumeError()
that's the case you can use , which is just a typeguard workingassertError()
in the same way as .
assertError() is to prefer over assumeError(), but there might be situations
where you just want to type-guard and not risking ending up with something
throwing an error.
NOTE! assumeError() has no runtime-effect. It does nothing.
`ts
import { assumeError } from '@poppanator/assert-error'
try {
// Do some funky gaspacho
} catch (err: unknown) {
assumeError(err)
console.error('Error:', err.message)
// These two are the same thing
assumeError
assumeError(err, MyError)
if (err.code) {
console.error('Error code:', err.code)
}
}
``