tswrap

Random assortment of Typescript utilities, wrappers, and types.

Premise

Ditch the required usage of try/catch for async/await functions.

Return errors normally, utilise typescript types to force errors to be handled.

Usage

Install it: npm install tswrap --save

Require it: import * as tswrap from 'tswrap'

API

tswrap.R<ReturnType>

Shorthand for Promise<NodeJS.ErrnoException | T> Where T is a possible return type.

Best paired with an async function.

async function getItemById (id: string): tswrap.R<Item> {
  return database.lookup(id)
}

Functions marked with this return type always may return an error, and should be handled accordingly.

tswrap.RE

A utility function to mark that a function returns a promise that may return an error, but no other values you care about.

Equivalent to tswrap.R<null>.

tswrap.isError(value)

This function is used to check if the value returned from a function that has the return type of tswrap.R is an actual error.

If this function returns true, typescript knows the value is of type tswrap.E. If false, typescript knows the value is of the type T that was passed into tswrap.R<T>.

async function setPlayerConfirmedStatus (status: boolean): T.R<Player> {
  ...
}

const playerUpdateResult = await setPlayerConfirmedStatus(true)

// playerUpdateResult type here is `tswrap.E | Player`
// Trying to access the variable as a `Player` will result in an error.

if (T.isError(playerUpdateResult)) {
  // We have now narrowed the type of playerUpdateResult
  // to `tswrap.E`, and can handle that appropriately.
  console.error(`Error updating player: ${playerUpdateResult}`)
  return playerUpdateResult
}

// As long as we `return` from inside `isError`, typescript
// now knows that playerUpdateResult can no longer be `tswrap.E`,
// and as such, narrows the type back to `Player`.
console.log('Player email:', player.email)

tswrap.wrapPromise<ReturnType>(promise)

This function is used to wrap external promises that do not conform to the tswrap.R return type.

function updatePlayerEmail (id: string, email: string): Promise<Player> {
  return new Promise((resolve, reject) => {
    database.updatePlayer({ id }, { email }, (err, player) => {
      if (err) return reject(err)
      return resolve(player)
    })
  })
}

const playerUpdateResult = tswrap.wrapPromise<Player>(updatePlayerEmail(id, player))

if (tswrap.isError(playerUpdateResult)) {
  ...
}

tswrap.wrapAxios<ReturnType>(promise)

Higher level wrapper for axios results.

Will return either an AxiosError, or an AxiosResponse<ReturnType> value.

See tswrap.isAxiosError for an example.

tswrap.isAxiosError(value)

Used to check if the response from tswrap.wrapAxios is an AxiosError.

interface Response { id: string }

const result = await tswrap.wrapAxios<Response>(axios.get('https://my.com/api'))

if (T.isAxiosError(result)) {
  return result
}

// result.data is now typed to the parameter passed to `tswrap.wrapAxios`
console.log('Got ID:', result.data.id)

tswrap.parseData<ReturnType>(data, structure)

Used in conjunction with io-ts for doing runtime validation.

Wraps structure.decode() into a tswrap compliant function.

See tswrap.isParseError for an example.

tswrap.isParseError(value)

Used to check if the response from tswrap.parseData is an error.

const requestSchema = iots.interface({ id: iots.string })
type RequestSchemaType = iots.TypeOf<typeof requestSchema>

const request = { id: 123 }

const parsedData = tswrap.parseData<RequestSchemaType>(request, requestSchema)

if (T.isParseError(parsedData)) {
  // parsedData here is the raw Left<iots.Errors, any>
  // allowing you to use your own reporters to return an error
  return parsedData
}

console.log('Got ID:', parsedData.id)