Docs / API / Stdlib / Jsexn

JsExn

Provide utilities for dealing with JS exceptions.

JS exceptions can be of any type, even though they should be of type Error of one of its subclasses.

See throw on MDN.

t

RESCRIPT

type t = unknown

Represents a JS exception

fromException

RESCRIPT

let fromException: exn => option<t>

anyToExnInternal

RESCRIPT

let anyToExnInternal: 'a => exn

anyToExnInternal(obj) will take any value obj and wrap it in a JsExn if given value is not an exn already. If obj is an exn, it will return obj without any changes.

This function is mostly useful for cases where you want to unify a type of a value that potentially is either exn, a JS error, or any other JS value really (e.g. for a value passed to a Promise.catch callback)

IMPORTANT: This is an internal API and may be changed / removed any time in the future.

stack

RESCRIPT

let stack: t => option<string>

stack(jsExn) retrieves the stack property of the exception, if it exists. The stack is a list of what functions were called, and what files they are defined in, prior to the error happening.

See Error.prototype.stack on MDN.

Example

RESCRIPT
try {JsError.make("error")->JsError.throw} catch {
| JsExn(e) => Console.log(JsExn.stack(e)) // Logs `stack`
| _ => assert(false)
}

message

RESCRIPT

let message: t => option<string>

message(error) retrieves the message property of the error, if it exists.

See Error.prototype.message on MDN.

Example

RESCRIPT
try {JsError.SyntaxError.throwWithMessage("Some message here")} catch {
| JsExn(e) => e->JsExn.message->Option.getExn == "Some message here"
| _ => assert(false)
}

name

RESCRIPT

let name: t => option<string>

name(error) retrieves the name property of the error, if it exists.

See Error.prototype.name on MDN.

Example

RESCRIPT
try {JsError.SyntaxError.throwWithMessage("Some message here")} catch {
| JsExn(e) => e->JsExn.name->Option.getExn == "SyntaxError"
| _ => assert(false)
}

fileName

RESCRIPT

let fileName: t => option<string>

fileName(error) retrieves the fileName property of the error, if it exists.

See Error.prototype.fileName on MDN.

throw

RESCRIPT

let throw: 'a => 'b

Throws the given value, terminating execution unless caught by a surrounding try/catch block.

This is meant to be used when a JS API is based on throwing values that are not of type Error or its subclasses.

ignore

RESCRIPT

let ignore: t => unit

ignore(jsExn) ignores the provided JS exception and returns unit.

This helper is useful when you want to discard a value (for example, the result of an operation with side effects) without having to store or process it further.