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Radashi

isResult

Check if a value is a Result tuple

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Usage

Check if a value is a Result tuple.

Don’t know what that is? Read the Result section further down.

import * as _ from 'radashi'


_.isResult([undefined, 42]) // => true
_.isResult([new Error(), undefined]) // => true


// Tuple must be of length 2.
_.isResult([new Error()]) // => false
_.isResult([undefined, true, undefined]) // => false


// Non-tuple values are false.
_.isResult([]) // => false
_.isResult({}) // => false
_.isResult(null) // => false


// Result tuples cannot have both a value and an error.
_.isResult([new Error(), true]) // => false

Also see the related isResultOk and isResultErr functions.

Types In-Depth

Result

“Results” are tuples of 2 elements (an error and a result value).

  • The first element is always the error, or undefined if the operation was successful.
  • The second element is always the result value, unless an error occurred.
  • These tuples are represented by the Result<TResult, TError> type.
  • A default error type of Error is used when no error type is explicitly defined (e.g. Result<string>).

Ok and Err

There are 2 types of result: Ok<TResult> and Err<TError>.

  • The Ok type represents a successful operation. It’s a tuple of [undefined, TResult].
  • The Err type represents a failed operation. It’s a tuple of [TError, undefined].

The names “Ok” and “Err” are inspired by Rust’s std::result module.

To check for an Ok result, do this:

declare const value: unknown


if (isResult(value) && value[0] == null) {
  value // <-- now an Ok<unknown> type
  value[1] // <-- This is the resulting value!
}

To check for an Err result, do this:

declare const value: unknown


if (isResult(value) && value[0] != null) {
  value // <-- now an Err<Error> type
  value[0] // <-- This is the error!
}

You can also use the isResultOk and isResultErr functions to check for Ok and Err results respectively.