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Module

x/froebel/promisify.ts>default

A strictly typed utility library.
MathisBullinger/froebel
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variable default
import { default } from "https://deno.land/x/froebel@v0.21.3/promisify.ts";

Turns a function accepting a callback into a function returning a promise. You can specify in which parameter (if any) the callback expects to receive a result and in which it expects an error. Pass null to resultIndex or errorIndex if no result or errors are passed to the callback. By default the first argument passed to the callback is interpreted as result and none of the arguments as error (if the function accepting the callback throws or rejects, that will still result in the promisified function rejecting).

The callbackFirst property allows passing additional parameters after the callback and callbackLast will pass additional parameters before the callback.

Examples

Example 1

const notify = (cb: (msg: string) => void) => { msg('something') }
const waitForMessage = promisify(notify)
await waitForMessage()  // -> 'something'

// here result is passed at index 1 and errors at index 0.
const callbackAPI = (cb: (error?: Error, data?: unknown) => void) => {}
const asyncAPI = promisify(callbackAPI, 1, 0)

Example 2

const sleep = promisify(setTimeout).callbackFirst
await sleep(200)

Example 3

const fs = require('node:fs');
const stat = promisify(fs.stat, 1, 0).callbackLast

try {
  const stats = await stat('.');
  console.log(`This directory is owned by ${stats.uid}`);
} catch (err) {
  console.error(err)
}

type

<T extends λ, N extends number | null = 0>(
withCallback: T,
resultIndex?: N,
errorIndex?: number | null,
) => Promisified<T, N>