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Interface: TaskConstructor ​

The public interface for the Task class as a value: a constructor and the associated static properties.

Constructors ​

Constructor ​

new TaskConstructor<T, E>(executor): Task<T, E>

Construct a new Task, using callbacks to wrap APIs which do not natively provide a Promise.

This is identical to the Promise constructor, with one very important difference: rather than producing a value upon resolution and throwing an exception when a rejection occurs like Promise, a Task always “succeeds” in producing a usable value, just like Result for synchronous code.

For constructing a Task from an existing Promise, see:

For constructing a Task immediately resolved or rejected with given values, see Task.resolve and Task.reject respectively.

Parameters ​

executor ​

(resolve, reject) => void

A function which the constructor will execute to manage the lifecycle of the Task. The executor in turn has two functions as parameters: one to call on resolution, the other on rejection.

Returns ​

Task<T, E>

reject() ​

Call Signature ​

reject<T, E>(): Task<T, Unit>

Construct a Task which is already rejected. Useful when you have an error already, but need it to be available in an API which expects a Task.

Type Parameters ​
T ​

T = never

E ​

E extends object = { }

Returns ​

Task<T, Unit>

Call Signature ​

reject<T, E>(reason): Task<T, E>

Construct a Task which is already rejected. Useful when you have an error already, but need it to be available in an API which expects a Task.

Type Parameters ​
T ​

T = never

E ​

E = unknown

Parameters ​
reason ​

E

Returns ​

Task<T, E>

resolve() ​

Call Signature ​

resolve<T, E>(): Task<Unit, E>

Construct a Task which is already resolved. Useful when you have a value already, but need it to be available in an API which expects a Task.

Type Parameters ​
T ​

T extends Unit

E ​

E = never

Returns ​

Task<Unit, E>

Call Signature ​

resolve<T, E>(value): Task<T, E>

Construct a Task which is already resolved. Useful when you have a value already, but need it to be available in an API which expects a Task.

Type Parameters ​
T ​

T

E ​

E = never

Parameters ​
value ​

T

Returns ​

Task<T, E>

withResolvers() ​

withResolvers<T, E>(): WithResolvers<T, E>

Create a pending Task and supply resolveWith and rejectWith helpers, similar to the Promise.withResolvers static method, but producing a Task with the usual safety guarantees.

Examples ​

Resolution ​

ts
let { task, resolveWith, rejectWith } = Task.withResolvers<string, Error>();
resolveWith("Hello!");

let result = await task.map((s) => s.length);
let length = result.unwrapOr(0);
console.log(length); // 5

Rejection ​

ts
let { task, resolveWith, rejectWith } = Task.withResolvers<string, Error>();
rejectWith(new Error("oh teh noes!"));

let result = await task.mapRejection((s) => s.length);
let errLength = result.isErr ? result.error : 0;
console.log(errLength); // 5

Type Parameters ​

T ​

T

E ​

E

Returns ​

WithResolvers<T, E>