How to use async/await without try/catch block

How to use async await without try-catch block.md

How to use async/await without try/catch block

We can use something like this:

async function resolveToNumber () {
  const promise = Promise.resolve(1)
  const [error, result] = await to(promise)
  console.log(error, result) // [null, 1] -> Here we have the result, and error will be null
}

async function resolveToString () {
  const promise = Promise.resolve("a")
  const [error, result] = await to(promise)
  console.log(error, result) // [null, "a"] -> Here we have the result, and error will be null
}

async function resolveToObject () {
  const promise = Promise.resolve({ a: 1, b: 2 })
  const [error, result] = await to(promise)
  console.log(error, result) // [null, { a: 1, b: 2 }] -> Here we have the result, and error will be null
}

async function rejected () {
  const promise = Promise.reject(1)
  const [error, result] = await to(promise)
  console.log(error, result) // [Error, null] -> Here he have Error, and result will be null
}

How we implement the function to?

Vanilla JavaScript

In regular JavaScript, just create the function like this:

const to = p => p.then(r => [null, r]).catch(e => [e])

TypeScript

If you are using TypeScript, there are a few more ways to do the same thing.

First, we declare the possible return types:

type ErrorTuple = [Error, null]
type SuccessTuple <T> = [null, T]

Then, we can go this way:

async function to <T>(promise: Promise<T>) {
  return promise
    .then(r => [null, r] as SuccessTuple<T>)
    .catch(e => [e, null] as ErrorTuple)
}

Or this way:

async function to <T>(promise: Promise<T>): Promise<ErrorTuple | SuccessTuple<T>> {
  return promise
    .then<SuccessTuple<T>>(r => [null, r])
    .catch<ErrorTuple>(e => [e, null])
}

Or this way:

async function to <T>(promise: Promise<T>): Promise<ErrorTuple | SuccessTuple<T>> {
  return promise
    .then<SuccessTuple<T>, ErrorTuple>(
      r => [null, r], 
      e => [e, null]
    )
}

Or yet, this way:

async function to <T>(promise: Promise<T>): Promise<ErrorTuple | SuccessTuple<T>> {
  try {
    const result = await promise
    return [null, result]
  } catch (e) {
    return [e, null]
  }
}