True Myth / task / safelyTryOrElse

Variable: safelyTryOrElse()

const safelyTryOrElse: {<T, E>(onError, fn): Task<T, E>; <T, E>(onError): (fn) => Task<T, E>; } = tryOrElse

An alias for tryOrElse for ease of migrating from v8.x to v9.x.

TIP

You should switch to tryOrElse. We expect to deprecate and remove this alias at some point!

Call Signature

<T, E>(onError, fn): Task<T, E>

Given a function which takes no arguments and returns a PromiseLike and a function which accepts an unknown rejection reason and transforms it into a known rejection type E, return a Task<T, E> for the result of invoking that function. This safely handles functions which fail synchronously or asynchronously, so unlike fromPromise is safe to use with values which may throw errors before producing a Promise.

Examples

import { tryOrElse } from 'true-myth/task';

function throws(): Promise<number> {
  throw new Error("Uh oh!");
}

// Note: passing the function by name, *not* calling it.
let theTask = tryOrElse(
  (reason) => `Something went wrong: ${reason}`,
  throws
);
let theResult = await theTask;
console.log(theResult.toString); // Err("Something went wrong: Error: Uh oh!")

You can also write this in “curried” form, passing just the fallback value and getting back a function which accepts the:

import { tryOrElse } from 'true-myth/task';

function throws(): Promise<number> {
  throw new Error("Uh oh!");
}

// Note: passing the function by name, *not* calling it.
let withFallback = tryOrElse<number, string>(
  (reason) => `Something went wrong: ${reason}`
);
let theResult = await withFallback(throws);
console.log(theResult.toString); // Err("Something went wrong: Error: Uh oh!")

Note that in the curried form, you must specify the expected T type of the resulting Task, or else it will always be unknown.

Type Parameters

T

T

E

E

Parameters

onError

(reason) => E

The function to use to transform the rejection reasons if the PromiseLike produced by fn rejects.

fn

() => PromiseLike<T>

A function which returns a PromiseLike when called.

Returns

Task<T, E>

A Task which resolves to the resolution value of the promise or rejects with the rejection value of the promise or any error thrown while invoking fn.

Call Signature

<T, E>(onError): (fn) => Task<T, E>

Given a function which takes no arguments and returns a PromiseLike and a function which accepts an unknown rejection reason and transforms it into a known rejection type E, return a Task<T, E> for the result of invoking that function. This safely handles functions which fail synchronously or asynchronously, so unlike fromPromise is safe to use with values which may throw errors before producing a Promise.

Examples

import { tryOrElse } from 'true-myth/task';

function throws(): Promise<number> {
  throw new Error("Uh oh!");
}

// Note: passing the function by name, *not* calling it.
let theTask = tryOrElse(
  (reason) => `Something went wrong: ${reason}`,
  throws
);
let theResult = await theTask;
console.log(theResult.toString); // Err("Something went wrong: Error: Uh oh!")

You can also write this in “curried” form, passing just the fallback value and getting back a function which accepts the:

import { tryOrElse } from 'true-myth/task';

function throws(): Promise<number> {
  throw new Error("Uh oh!");
}

// Note: passing the function by name, *not* calling it.
let withFallback = tryOrElse<number, string>(
  (reason) => `Something went wrong: ${reason}`
);
let theResult = await withFallback(throws);
console.log(theResult.toString); // Err("Something went wrong: Error: Uh oh!")

Note that in the curried form, you must specify the expected T type of the resulting Task, or else it will always be unknown.

Type Parameters

T

T

E

E

Parameters

onError

(reason) => E

The function to use to transform the rejection reasons if the PromiseLike produced by fn rejects.

Returns

A Task which resolves to the resolution value of the promise or rejects with the rejection value of the promise or any error thrown while invoking fn.

(fn): Task<T, E>

Parameters

fn

() => PromiseLike<T>

Returns

Task<T, E>